Q&A Hero

Q: If a wheel turning at a constant rate completes 100 revolutions in 10 s its angular speed is: A) 0.31 rad/s B) 0.63 rad/s C) 10 rad/s D) 31 rad/s E) 63 rad/s

Q: If a wheel is turning at 3.0 rad/s, the time it takes to complete one revolution is about: A) 0.33 s B) 0.67 s C) 1.0 s D) 1.3 s E) 2.1 s

Q: An object rotates from 1to 2through an angle that is less than 2Ï€ radians. Which of the following represents its angular displacement?A) 1B) 2C) 1- 2D) 2- 1E) 1+ 2

Q: One-dimensional linear position is measured along a line, from a point designated x= 0. One-dimensional angular position:A) is measured along a line, from a point designated = 0.B) is measured along the axis of rotation.C) is the angle that an internal reference line makes with a fixed external reference line.D) is measured relative to the positive yaxis.E) is meaningless, as rotations take place in two dimensions.

Q: If a wheel turns with constant angular speed then: A) each point on its rim moves with constant velocity B) each point on its rim moves with constant acceleration C) the wheel turns through equal angles in equal times D) the angle through which the wheel turns in each second increases as time goes on E) the angle through which the wheel turns in each second decreases as time goes on

Q: One revolution per minute is about: A) 0.0524 rad/s B) 0.105 rad/s C) 0.95 rad/s D) 1.57 rad/s E) 6.28 rad/s

Q: One revolution is the same as:A) 1 radB) 57 radC) /2 radD)radE) 2rad

Q: A radian is about:A) 25°B) 37°C) 45°D) 57°E) 90°

Q: A cart loaded with sand slides forward along a horizontal frictionless track. As the cart moves, sand trickles out at a constant rate through a hole in the back of the cart. The acceleration of the cart is: A) constant and in the forward direction B) constant and in the backward direction C) variable and in the forward direction D) variable and in the backward direction E) zero

Q: A 1000-kg space probe is motionless in space. To start moving, its main engine is fired for 5 s during which time it ejects exhaust gases at 5000 m/s. At the end of this process it is moving at 20 m/s. The approximate mass of the ejected gas is: A) 0.8 kg B) 4 kg C) 5 kg D) 20 kg E) 25 kg

Q: A rocket exhausts fuel with a velocity of 1500 m/s, relative to the rocket. It starts from rest in outer space with fuel comprising 80 per cent of the total mass. When all the fuel has been exhausted its speed is: A) 3600 m/s B) 2400 m/s C) 1200 m/s D) 880 m/s E) 400 m/s

Q: At one instant of time a rocket is traveling in outer space at 2500 m/s and is exhausting fuel at a rate of 100 kg/s. If the speed of the fuel as it leaves the rocket is 1500 m/s, relative to the rocket, the thrust is:A) 0 NB) 1.0 x105NC) 1.5 x105ND) 2.9 x105NE) 2.5 x105N

Q: The thrust of a rocket is A) a gravitational force acting on the rocket B) the force of the exiting fuel gases on the rocket C) any force that is external to the rocket-fuel system D) a force that arises from the reduction in mass of the rocket-fuel system E) none of the above

Q: A hockey puck of mass m traveling along the xaxis at 4.5 m/s hits another identical hockey puck at rest. If after the collision the second puck travels at a speed of 3.5 m/s at an angle of 30 above the xaxis, is this an elastic collision? A) Yes, since momentum is conserved. B) No, since momentum is not conserved. C) Yes, since kinetic energy is conserved. D) No, since kinetic energy is not conserved. E) Not enough information.

Q: A hockey puck of mass m traveling along the xaxis at 4.5 m/s hits another identical hockey puck at rest. If after the collision the second puck travels at a speed of 3.5 m/s at an angle of 30 above the xaxis, what is the final velocity of the first puck? A) 1.0 m/s, 30 below the x axis B) 2.3 m/s, 50 below the x axis C) 2.8 m/s, 60 below the x axis D) 3.0 m/s, 45 below the x axis E) not enough information

Q: If a projectile hits a stationary target, and the projectile continues to travel in the same direction, A) the mass of the projectile is less than the mass of the target. B) the mass of the projectile is equal to the mass of the target. C) the mass of the projectile is greater than the mass of the target. D) nothing can be said about the masses of the projectile and target without further information. E) this is an unphysical situation and will not actually happen.

Q: If a projectile hits a stationary target, and the projectile rebounds and travels back the way it came, A) the mass of the projectile is much less than the mass of the target. B) the mass of the projectile is equal to the mass of the target. C) the mass of the projectile is much greater than the mass of the target. D) nothing can be said about the masses of the projectile and target without further information. E) this is an unphysical situation and will not actually happen.

Q: If a projectile hits a stationary target, and the projectile stops while the target moves at the same speed as the incoming speed of the projectile, A) the mass of the projectile is much less than the mass of the target. B) the mass of the projectile is equal to the mass of the target. C) the mass of the projectile is much greater than the mass of the target. D) nothing can be said about the masses of the projectile and target without further information. E) this is an unphysical situation and will not actually happen.

Q: Two objects, X and Y, are held at rest on a horizontal frictionless surface and a spring is compressed between them. The mass of X is 2/5 times the mass of Y. Immediately after the spring is released, X has a kinetic energy of 50 J and Y has a kinetic energy of: A) 20 J B) 8 J C) 310 J D) 125 J E) 50 J

Q: When a particle suffers a head-on elastic collision with another particle, initially at rest, the greatest fraction of kinetic energy is transferred if: A) the incident particle is initially traveling very fast B) the incident particle is traveling very slowly C) the incident particle is much more massive than the target particle D) the incident particle is much less massive than the target particle E) the incident and target particle have the same mass

Q: Blocks A and B are moving toward each other along the xaxis. A has a mass of 2.0 kg and a velocity of 50 m/s, while B has a mass of 4.0 kg and a velocity of -25 m/s. They suffer an elastic collision and move off along the xaxis. The kinetic energy transferred from A to B during the collision is:A) 0 JB) 2500 JC) 5000 JD) 7500 JE) 10000 J

Q: Sphere A has mass mand is moving with velocity v. It makes a head-on elastic collision with a stationary sphere B of mass 2m. After the collision their speeds (vA, vB) are:A) 0, v/2B) -v/3, 2v/3C) -v, vD) -2v/3, v/3E) none of these

Q: A very massive object traveling at 10 m/s strikes a light object, initially at rest, and the light object moves off in the direction of travel of the heavy object. If the collision is elastic, the speed of the lighter object is A) 5.0 m/s B) 10 m/s C) 15 m/s D) 20 m/s E) Can't tell from the information given.

Q: Block A, with a mass of 2.0 kg, moves along the xaxis with a velocity of 5.0 m/s in the positive x direction. It suffers an elastic collision with block B, initially at rest, and the blocks leave the collision along the xax is. If B is much more massive than A, the velocity of A after the collision is:A) 0 m/sB) +5.0 m/sC) -5.0 m/sD) +10 m/sE) -10 m/s

Q: Object A strikes the stationary object B head-on in an elastic collision. The mass of A is fixed, you may choose the mass of B appropriately. Then: A) for B to have the greatest recoil speed, choose mB= mA B) for B to have the greatest recoil momentum, choose mB<<mA C) for B to have the greatest recoil kinetic energy, choose mB>>mA D) for B to have the least recoil speed, choose mB= mA E) for B to have the greatest recoil kinetic energy, choose mB= mA

Q: Two carts (A and B), having spring bumpers, collide as shown. Cart A has a mass of 2 kg and is initially moving to the right. Cart B has a mass of 3 kg and is initially stationary. When the separation between the carts is a minimum: A) cart B is still at rest B) cart A has come to rest C) the carts have the same momentum D) the carts have the same kinetic energy E) the kinetic energy of the system is at a minimum

Q: The law of conservation of momentum applies to a system of colliding objects only if: A) there is no change in kinetic energy of the system B) the coefficient of restitution is one C) the coefficient of restitution is zero D) the net external impulse is zero E) the collisions are all elastic

Q: A projectile in flight explodes into several fragments. The total momentum of the fragments immediately after this explosion: A) is the same as the momentum of the projectile immediately before the explosion B) has been changed into kinetic energy of the fragments C) is less than the momentum of the projectile immediately before the explosion D) is more than the momentum of the projectile immediately before the explosion E) has been changed into radiant energy

Q: A block moves at 5 m/s in the positive xdirection and hits an identical block, initially at rest. A small amount of gunpowder had been placed on one of the blocks. The explosion does not harm the blocks but it doubles their total kinetic energy. After the explosion the blocks move along the xaxis and the incident block has a speed of: A) 1.8 m/s B) 3.2 m/s C) 5.0 m/s D) 6.8 m/s E) 7.1 m/s

Q: Two identical carts travel at 1 m/s on a common surface. They collide head-on and are reported to rebound, each with a speed of 2 m/s. Then: A) momentum was not conserved, therefore the report must be false B) if some other form of energy were changed to kinetic during the collision, the report could be true C) if the collision were elastic, the report could be true D) if the surface were inclined, the report could be true E) kinetic energy increased, therefore the report must be false

Q: A 2-kg cart, traveling on a horizontal air track with a speed of 3 m/s, collides with a stationary 4-kg cart. The carts stick together. The impulse exerted by one cart on the other has a magnitude of:A) 0 N sB) 4 N sC) 6 N sD) 9 N sE) 12 N s

Q: For a completely inelastic two-body collision the kinetic energy retained by the objects is the same as: A) the total kinetic energy before the collision B) the difference in the kinetic energies of the objects before the collision C) 1/2Mv2com, where Mis the total mass and vcomis the velocity of the center of mass D) the kinetic energy of the more massive body before the collision E) the kinetic energy of the less massive body before the collision

Q: Blocks A and B are moving toward each other. A has a mass of 2.0 kg and a velocity of 50 m/s, while B has a mass of 4.0 kg and a velocity of "25 m/s. They suffer a completely inelastic collision. The kinetic energy lost during the collision is: A) 0 J B) 1250 J C) 3750 J D) 5000 J E) 5600 J

Q: A 3.0-kg cart and a 2.0-kg cart approach each other on a horizontal air track. They collide and stick together. After the collision their total kinetic energy is 40 J. The speed of their center of mass is: A) 0 m/s B) 2.8 m/s C) 4.0 m/s D) 5.2 m/s E) 8.0 m/s

Q: A 3-g bullet is fired horizontally into a 10-kg block of wood suspended by a rope from the ceiling. The block swings in an arc, rising 3 mm above its lowest position. The velocity of the bullet was:A) unknown since the heat generated in the collision was not givenB) 8.0 x102m/sC) 24.0 m/sD) 8.0 m/sE) 2.4 x104m/s

Q: A 3.00-g bullet traveling horizontally at 400 m/s hits a 3.00-kg wooden block, which is initially at rest on a smooth horizontal table. The bullet buries itself in the block without passing through. The speed of the block after the collision is: A) 1.33 m/s B) 0.40 m/s C) 12.0 m/s D) 12.6 m/s E) 40.0 m/s

Q: A 500-kg sack of coal is dropped on a 2000-kg railroad flatcar which was initially moving at 3 m/s as shown. After the sack rests on the flatcar, the speed of the flatcar is: A) 0.6 m/s B) 1.2 m/s C) 1.8 m/s D) 2.4 m/s E) 3.6 m/s

Q: Cart A, with a mass of 0.2 kg, travels on a horizontal air track at 3 m/s and hits cart B, which has a mass of 0.4 kg and is initially at rest. After the collision the center of mass of the two cart system has a speed in m/s of: A) 0 m/s B) 1.0 m/s C) 2.3 m/s D) 2.5 m/s E) 5.0 m/s

Q: Bullets from two revolvers are fired with the same velocity. The bullet from gun #1 is twice as heavy as the bullet from gun #2. Gun #1 weighs three times as much as gun #2. The ratio of the momentum imparted to gun #1 to that imparted to gun #2 is: A) 2:3 B) 3:2 C) 2:1 D) 3:1 E) 6:1

Q: A rifle of mass M is initially at rest but free to recoil. It fires a bullet of mass m and velocity v (relative to the ground). After firing, the velocity of the rifle (relative to the ground) is:A) -mvB) -Mv/mC) -mv/MD) -vE) mv/M

Q: Two spacemen are floating together with zero speed in a gravity-free region of space. The mass of spaceman A is 120 kg and that of spaceman B is 90 kg. Spaceman A pushes B away from him with B attaining a final speed of 0.5 m/s. The final recoil speed of A is: A) 0 m/s B) 0.38 m/s C) 0.43 m/s D) 0.50 m/s E) 1.0 m/s

Q: A man is marooned at rest on level frictionless ice. In desperation, he hurls his shoe to the right at 15 m/s. If the man weighs 720 N and the shoe weighs 4.0 N, the man moves to the left at approximately:A) 0 m/sB) 2.1 x10-2m/sC) 8.3 x10-2m/sD) 15 m/sE) 1.1 m/s

Q: A 64-kg woman stands on frictionless level ice with a 0.10-kg stone at her feet. She kicks the stone with her foot so that she acquires a velocity of 0.0017 m/s in the forward direction. The velocity acquired by the stone is: A) 1.1 m/s forward B) 1.1 m/s backward C) 0.0017 m/s forward D) 0.0017 m/s backward E) none of these

Q: In a one-dimensional collision, A) a moving object strikes a stationary object, after which the objects move in arbitrary directions. B) the objects must be moving along the same line before the collision, but may be moving in arbitrary directions after the collision. C) one of the objects must remain at rest after the collision. D) one of the objects must be at rest before the collision. E) all motion, both before and after the collision, must be along the same line.

Q: Whenever an object strikes a stationary object of equal mass: A) the two objects cannot stick together B) the collision must be elastic C) the first object must stop D) momentum is not necessarily conserved E) none of the above

Q: An elastic collision is one in which: A) momentum is not conserved but kinetic energy is conserved B) total mass is not conserved but momentum is conserved C) kinetic energy and momentum are both conserved D) momentum is conserved but kinetic energy is not conserved E) the total impulse is equal to the change in kinetic energy

Q: A 4.0-N puck is traveling at 3.0 m/s. It strikes an 8.0-N puck, which is stationary. The two pucks stick together. Their common final speed is: A) 1.0 m/s B) 1.5 m/s C) 2.0 m/s D) 2.3 m/s E) 3.0 m/s

Q: An inelastic collision is one in which: A) momentum is not conserved but kinetic energy is conserved B) total mass is not conserved but momentum is conserved C) neither kinetic energy nor momentum is conserved D) momentum is conserved but kinetic energy is not conserved E) the total impulse is equal to the change in kinetic energy

Q: A shell is launched from a cannon and explodes mid-air. Which of the following is correct after the explosion? A) Since the explosion exerts external forces on the shell, neither its horizontal momentum nor its vertical momentum is conserved. B) Since the explosion exerts only internal forces on the shell, both its horizontal and vertical momenta are conserved. C) Since the explosion exerts only internal forces on the shell, but gravity is an external force, neither its horizontal momentum nor its vertical momentum is conserved. D) Since the explosion exerts only internal forces on the shell, but gravity is an external force, its horizontal momentum is conserved but its vertical momentum is not conserved. E) Since the explosion exerts only internal forces on the shell, but gravity is an external force, its vertical momentum is conserved but its horizontal momentum is not conserved.

Q: A 75-kg man is riding in a 30-kg cart at 2.0 m/s. He jumps off in such a way as to land on the ground with no horizontal velocity. The resulting change in speed of the cart is: A) 0 m/s B) 2.0 m/s C) 3.0 m/s D) 5.0 m/s E) 7.0 m/s

Q: A stream of gas consists of n molecules. Each molecule has mass mand speed v. The stream is reflected elastically from a rigid surface as shown. The magnitude of the change in the total momentum of the stream is:A) 2mnvB) 2mnvsin 30°C) mnvsin 30°D) mnvcos 30°E) mnv

Q: The plot shows the force acting on an object as a function of time. Over the time the force is applied, the total impulse is:A) 0 N sB) 2 N sC) 4 N sD) 8 N sE) cannot be determined without knowing the mass of the object

Q: The force on a particle is given by F(t) = 0.71 t+ 1.2 t2, in N. If the force acts from t = 0 to t = 2.0 s, the total impulse is:A) 1.2 kg m/sB) 1.9 kg m/sC) 4.6 kg m/sD) 4.8 kg m/sE) 6.2 kg m/s

Q: A 25-kg box of books is dropped on the floor from a height of 1.1 m and comes to rest. What impulse did the floor exert on the box?A) cannot be answered without knowing how long it took the box to stopB) 22 kg m/sC) 120 kg m/sD) 270kg m/s

Q: A student's life was saved in an automobile accident because an airbag expanded in front of his head. If the car had not been equipped with an airbag, the windshield would have stopped the motion of his head in a much shorter time. Compared to the windshield, the airbag: A) causes a much smaller change in momentum B) exerts a much smaller impulse C) causes a much smaller change in kinetic energy D) exerts a much smaller force E) does much more work

Q: Two bodies of unequal mass, placed at rest on a frictionless surface, are acted on by equal horizontal forces for equal times. Just after these forces are removed, the body of greater mass will have: A) greater speed than the other body B) greater acceleration than the other body C) smaller momentum than the other body D) greater momentum than the other body E) the same momentum as the other body

Q: Sphere X, of mass 2 kg, is moving to the right at 10 m/s. Sphere Y, of mass 4 kg, is moving to the left at 10 m/s. The two spheres collide head-on. The magnitude of the impulse of X on Y is: A) twice the magnitude of the impulse of Y on X B) half the magnitude of the impulse of Y on X C) one-fourth the magnitude of the impulse of Y on X D) four times the magnitude of the impulse of Y on X E) the same as the magnitude of the impulse of Y on X

Q: A 640-N acrobat falls 5.0 m from rest into a net. The net tosses him back up with the same speed he had just before he hit the net. The average upward force exerted on him by the net during this collision is: A) 32 N B) 64 N C) 320 N D) 640 N E) impossible to determine from given data

Q: A golf ball of mass mis hit by a golf club so that the ball leaves the tee with speed v. The club is in contact with the ball for time T. The average force on the club on the ball during the time Tis: A) mvT B) mv/T C) (1/2)mv2T D) mv2/(2T) E) mT2/(2v)

Q: What magnitude impulse will give a 2.0-kg object a momentum change of magnitude +50 kg m/s?A) + 25 N sB) - 25 N sC) + 50 N sD) - 50 N sE) + 100 N s

Q: A uniform narrow bar, resting on frictionless ice, is given a transverse horizontal impulse at one end as shown. The center of mass of the bar COM will then: A) remain at rest B) move in a circle C) move in a straight line D) move in a parabola E) move along some other curve

Q: A 10-kg block of ice is at rest on a frictionless horizontal surface. A 1.0-N force is applied in an easterly direction for 1.0 s. During this time interval, the block:A) acquires a speed of 1 m/sB) moves 10 cmC) acquires a momentum of 1.0 kg m/sD) acquires a kinetic energy of 0.1 JE) none of the above

Q: A 0.3 kg rubber ball is dropped from the window of a building. It strikes the sidewalk below at 30 m/s and rebounds up at 20 m/s. The magnitude of the impulse due to the collision with the sidewalk is:A) 3.0 N sB) 6.0 N sC) 9.0 N sD) 15 N sE) 29 N s

Q: The physical quantity "impulse" has the same dimensions as that of: A) force B) power C) energy D) momentum E) work

Q: A 5-kg object can move along the xaxis. It is subjected to a force in the positive xdirection; a graph of Fas a function of time tis shown below. Over the time the force is applied the change in the velocity of the object is: A) 0.8 m/s B) 1.3 m/s C) 1.6 m/s D) 2.3 m/s E) 4.0 m/s

Q: The direction of the impulse on a struck baseball A) depends on how fast the ball was thrown B) is in the direction of the ball's change in velocity C) is in the direction of the force of gravity D) depends on how hard the ball is struck E) Impulse is a scalar, and does not have a direction associated with it.

Q: The momentum of a system of particles is changing at the rate of 0.71 t+ 1.2 t2, in kg m/s. The net force at t= 2.0 sA) cannot be determined without knowing the masses of the particles.B) is 5.5 NC) is 3.1 ND) is 1.9 NE) cannot be determined without knowing the momentum at t= 0

Q: The acceleration of the center of mass of a system of particles: A) depends on all the forces on all the particles B) depends on all the velocities of all the particles C) depends only on the forces external to the system of particles D) depends only on the forces internal to the system of particles E) depends only on the force of gravity

Q: Block A, with a mass of 4.0 kg, is moving with a speed of 2.0 m/s while block B, with a mass of 8.0 kg, is moving in the opposite direction with a speed of 3.0 m/s. The momentum of the center of mass of the two-block system is: A) 16 m/s in the same direction as A B) 16 m/s in the same direction as B C) 32 m/s in the same direction as A D) 12 m/s in the same direction as B E) 60 m/s in the same direction as A

Q: Force: A) equals the negative integral (with respect to distance) of the potential energy function B) is the ability to do work C) is the rate of change of doing work D) equals the time rate of change of momentum E) has dimensions of momentum multiplied by time

Q: For a two-body collision, involving objects with different masses, a frame of reference which has the same velocity relative to the laboratory as does the center of mass of the two objects is: A) a frame for which the momentum of the incident object is zero B) a frame for which the momentum of the target object is zero C) a frame for which the average momentum of the two objects is zero D) a frame for which the total momentum of the two objects is zero E) none of the above

Q: When you step on the accelerator to increase the speed of your car, the force that accelerates the car is: A) the force of your foot on the accelerator B) the force of friction of the road on the tires C) the force of the engine on the drive shaft D) the normal force of the road on the tires E) none of the above

Q: If the total momentum of a system is changing: A) particles of the system must be exerting forces on each other B) the system must be under the influence of gravity C) the center of mass must have constant velocity D) a net external force must be acting on the system E) none of the above

Q: A particle moves along the xaxis. Its momentum is graphed below as a function of time. Rank the numbered regions according to the magnitude of the force acting on the particle, least to greatest. A) 1, 2, 3, 4 B) 2, 3, 4, 1 C) 1, 4, 3, 2 D) 4, 3, 2, 1 E) 2, 4, 3, 1

Q: A ball hits a wall and rebounds with the same speed, as diagrammed below. The changes in the components of the momentum of the ball are:A) px> 0, py> 0B) px< 0, py> 0C) px= 0, py> 0D) px= 0, py< 0E) px> 0, py< 0

Q: A 1.0 kg-ball moving at 2.0 m/s perpendicular to a wall rebounds from the wall at 1.5 m/s. The change in the momentum of the ball is:A) zeroB) 0.5 N s away from wallC) 0.5 N s toward wallD) 3.5 N s away from wallE) 3.5 N s toward wall

Q: A 2.5-kg stone is released from rest and falls toward Earth. After 4.0 s, the magnitude of its momentum is:A) 98 kg m/sB) 78 kg m/sC) 39 kg m/sD) 24 kg m/sE) 0 kg m/s

Q: Two objects, P and Q, have the same momentum. Q can have more kinetic energy than P if it: A) weighs more than P B) is moving faster than P C) weighs the same as P D) is moving slower than P E) is moving at the same speed as P

Q: Two bodies, A and B, have equal kinetic energies. The mass of A is nine times that of B. The ratio of the momentum of A to that of B is: A) 1:9 B) 1:3 C) 1:1 D) 3:1 E) 9:1

Q: The momentum of an object at a given instant is independent of its: A) inertia B) mass C) speed D) velocity E) acceleration