Q&A Hero

Q: An object is raised from the surface of Earth to a height of two Earth radii above Earth. Then: A) its mass increases and its weight remains constant B) both its mass and weight remain constant C) its mass remains constant and its weight decreases D) both its mass and its weight decrease E) its mass remains constant and its weight increases

Q: An object at the surface of Earth (at a distance Rfrom the center of Earth) weighs 90 N. Its weight at a distance 3Rfrom the center of Earth is: A) 10 N B) 30 N C) 90 N D) 270 N E) 810 N

Q: Let Mdenote the mass of Earth and let Rdenote its radius. The ratio g/Gat Earth's surface is: A) R2/M B) M/R2 C) MR2 D) M/R E) R/M

Q: A spherical shell has inner radius R1, outer radius R2, and mass M, distributed uniformly throughout the shell. The magnitude of the gravitational force exerted on the shell by a point mass particle of ma distance d from the center, outside the outer radius, is:A) 0B) C) GMm/d2D) E) GMm/(R1- d)2

Q: Four particles, each with mass m,are arranged symmetrically about the origin on the xaxis. A fifth particle, with mass M, is on the yaxis. The direction of the gravitational force on Mis:

Q: Three particles, two with mass mand one mass M, might be arranged in any of the four configurations known below. Rank the configurations according to the magnitude of the gravitational force on M, least to greatest. A) 1, 2, 3, 4 B) 2, 1, 3, 4 C) 2, 1, 4, 3 D) 2, 3, 4, 2 E) 2, 3, 2, 4

Q: An astronaut on the Moon simultaneously drops a feather and a hammer. The fact that they land together shows that: A) no gravity forces act on a body in a vacuum B) the acceleration due to gravity on the Moon is less than gon the Earth C) in the absence of air resistance all bodies at a given location fall with the same acceleration D) the feather has a greater weight on the Moon than on Earth E) G= 0 on the Moon

Q: Let F1be the magnitude of the gravitational force exerted on the Sun by Earth and F2be the magnitude of the force exerted on Earth by the Sun. Then: A) F1is much greater than F2 B) F1is slightly greater than F2 C) F1is equal to F2 D) F1is slightly less than F2 E) F1is much less than F2

Q: Earth exerts a gravitational force on the Moon, keeping it in its orbit. The reaction to this force, in the sense of Newton's third law, is: A) the centripetal force on the Moon B) the nearly circular orbit of the Moon C) the gravitational force exerted on Earth by the Moon D) the tides due to the Moon E) the apple hitting Newton on the head

Q: The magnitude of the acceleration of a planet in orbit around the Sun is proportional to: A) the mass of the planet B) the mass of the Sun C) the distance between the planet and the Sun D) the reciprocal of the distance between the planet and the Sun E) the product of the mass of the planet and the mass of the Sun

Q: The mass of an object: A) is slightly different at different locations on the Earth B) is a vector C) is independent of the acceleration due to gravity D) is the same for all objects of the same size and shape E) can be measured directly and accurately on a spring scale

Q: The gravitational constant Ghas the derived unitsA) N.mB) N.m/kgC) N.kg/mD) N.m2/kg2E) N.kg2/m2

Q: Suitable units for the gravitational constant Gare:A) kg.m/s2B) m/s2C) Ns./mD) kg.m/sE) m3/(kg.s2)

Q: In the formula F = Gm1m2/r2, the quantity G: A) depends on the local value of g B) is used only when the Earth is one of the two masses C) is greatest at the surface of the Earth D) is a universal constant of nature E) is related to the Sun in the same way that gis related to the Earth

Q: In Einstein's theory of gravitation, gravity is due to: A) the acceleration of the universe B) the presence of mass C) the rotation of the universe D) the curvature of spacetime E) the speed of light

Q: Einstein's principle of equivalence states: A) the gravitational constant is the same everywhere in the universe B) it is impossible to tell the difference between gravitational force and the normal force C) every mass exerts a gravitational force on every other mass D) gravitational mass and inertial mass are the same E) the laws of physics are the same in all inertial reference frames

Q: A planet in another solar system orbits a star with a mass of 4.0 x1030kg. At one point in its orbit it is 250 x106km from the star and is moving at 35 km/s. Take the universal gravitational constant to be 6.67 x10-11m2/s2.kg and calculate the semimajor axis of the planet's orbit. The result is:A) 79 x106kmB) 140 x106kmC) 290x106kmD) 320x106kmE) 590x106km

Q: A spaceship is returning to Earth with its engine turned off. Consider only the gravitational field of Earth.Let Mbe the mass of Earth, mbe the mass of the spaceship, and Rbe the distance from the center of Earth. In moving from position 1 to position 2 the kinetic energy of the spaceship increases by: A) B) C) D) E)

Q: An artificial satellite of Earth nears the end of its life due to air resistance. While still in orbit: A) it moves faster as the orbit lowers B) it moves slower as the orbit lowers C) it slowly spirals away from Earth D) it moves slower in the same orbit but with a decreasing period E) it moves faster in the same orbit but with an increasing period

Q: An artificial Earth satellite is moved from a circular orbit with radius Rto a circular orbit with radius 2R. During this move: A) the gravitational force does positive work, the kinetic energy of the satellite increases, and the potential energy of the Earth-satellite system increases B) the gravitational force does positive work, the kinetic energy of the satellite increases, and the potential energy of the Earth-satellite system decreases C) the gravitational force does positive work, the kinetic energy of the satellite decreases, and the potential energy of the Earth-satellite system increases D) the gravitational force does negative work, the kinetic energy of the satellite system increases, and the potential energy of the Earth-satellite system decreases E) the gravitational force does negative work, the kinetic energy of the satellite decreases, and the potential energy of the Earth-satellite system increases

Q: Assume that Earth is in circular orbit around the Sun with kinetic energy Kand potential energy U, taken to be zero for infinite separation. Then, the relationship between Kand U:A) is K= UB) is K= -UC) is K= U/2D) is K= -U/2E) depends on the radius of the orbit

Q: Given the perihelion distance, aphelion distance, and speed at perihelion of a planet, which of the following CANNOT be calculated? A) the mass of the star B) the mass of the planet C) the speed of the planet at aphelion D) the period of orbit E) the semimajor axis of the orbit

Q: Two planets are orbiting a star in a distant galaxy. The first has a semimajor axis of 150 x106km, an eccentricity of 0.20, and a period of 1.0 Earth years. The second has a semimajor axis of 250 x106km, an eccentricity of 0.30, and a period of:A) 0.46 Earth yrB) 0.57 Earth yrC) 1.4 Earth yrD) 1.7 Earth yrE) 2.8 Earth yr

Q: A cube with 2.0-cm sides is made of material with a bulk modulus of 4.7 ï‚´105N/m2. When it is subjected to a pressure of 2.0 ï‚´105Pa the length in cm of its any of its any of its sides is: A) 0.85 cm B) 1.15 cm C) 1.66 cm D) 2.0 cm E) none of these

Q: A cube with edges exactly 2 cm long is made of material with a bulk modulus of 3.5 x109N/m2. When it is subjected to a pressure of 3.0 x105Pa its volume is:A) 7.31 cm3B) 7.99931 cm3C) 8.00069 cm3D) 8.69 cm3E) none of these

Q: The bulk modulus is a proportionality constant that relates the pressure acting on an object to: A) the shear B) the fractional change in volume C) the fractional change in length D) Young's modulus E) the spring constant

Q: A shearing force of 50 N is applied to an aluminum rod with a length of 10 m, a cross-sectional area of 1.0 x10-­5m, and shear modulus of 2.5 x1010 N/m2.As a result the rod is sheared through a distance of:A) zeroB) 2.0 mmC) 2.0 cmD) 20 cmE) 2.0 m

Q: The ultimate strength of a sample is the stress at which the sample:A) returns to its original shape when the stress is removedB) remains underwaterC) breaksD) bends 180°E) does none of these

Q: Young's modulus can be used to calculate the strain for a stress that is: A) just below the ultimate strength B) just above the ultimate strength C) well below the yield strength D) well above the yield strength E) none of the above

Q: Two supports, made of the same material and initially of equal length, are 2.0 m apart. A stiff board with a length of 4.0 m and a mass of 10 kg is placed on the supports, with one support at the left end and the other at the midpoint. A block is placed on the board a distance of 0.50 m from left end.As a result the board is horizontal (that is, the downward force on each support is the same). The mass of the block is: A) 0 kg B) 2.3 kg C) 6.6 kg D) 10 kg E) 20 kg

Q: A 4.0 m steel beam with a cross sectional area of 1.0 x10-2m2and a Young's modulus of 2.0 x1011N/m2is wedged horizontally between two vertical walls. In order to wedge the beam, it is compressed by 0.020 mm. If the coefficient of static friction between the beam and the walls is 0.35, the maximum mass (including its own) it can bear without slipping is:A) 0 kgB) 36 kgC) 70 kgD) 360 kgE) 700 kg

Q: A force of 5000 N is applied outwardly to each end of a 5.0-m long rod with a radius of 34.0 mm and a Young's modulus of 125 x108N/m2. The elongation of the rod is:A) 0.022 mmB) 0.0040 mmC) 0.11 mmD) 0.55 mmE) 1.42 mm

Q: A certain wire stretches 0.90 cm when outward forces with magnitude Fare applied to each end. The same forces are applied to a wire of the same material but with three times the diameter and three times the length. The second wire stretches: A) 0.10 cm B) 0.30 cm C) 0.90 cm D) 2.7 cm E) 8.1 cm

Q: Young's modulus is a proportionality constant that relates the force per unit area applied perpendicularly at the surface of an object to: A) the shear B) the fractional change in volume C) the fractional change in length D) the pressure E) the spring constant

Q: If you sit on an ordinary 4-legged chair, which of the following is true? A) As long as you know your weight and the point at which it acts on the chair, you can calculate the forces exerted by all four chair legs on the floor. B) As long as you know your weight and the point at which it acts on the chair, you can calculate the forces exerted by all four chair legs on the floor, but only if your own feet are not also on the floor. C) This is an indeterminate situation, and the forces of the chair legs on the floor cannot be uniquely calculated. D) This is an indeterminate situation, and the forces of the chair legs on the floor cannot be uniquely calculated without knowing how your weight is distributed on the chair. E) This is an indeterminate situation, and the forces of the chair legs on the floor cannot be uniquely calculated without knowing how the chair deforms due to your weight.

Q: To shear a cube-shaped object, forces of equal magnitude and opposite directions might be applied: A) to opposite faces, perpendicular to the faces B) to opposite faces, parallel to the faces C) to adjacent faces, perpendicular to the faces D) to adjacent faces, neither parallel nor perpendicular to the faces E) to a single face, in any direction

Q: Young's modulus can be correctly given in:A) N.mB) N/m2C) N.m/sD) N/mE) joules

Q: Strain can be measured in:A) N/m2B) N.m2C) N/mD) N.mE) none of these (it is dimensionless)

Q: Stress can be measured in:A) N/m2B) N.m2C) N/mD) N.mE) none of these (it is dimensionless)

Q: The uniform rod shown below is held in place by the rope and wall. Suppose you know the weight of the rod and all dimensions. Then you can solve a single equation for the force exerted by the rope, provided you write expressions for the torques about the point: A) 1 B) 2 C) 3 D) 4 E) 1, 2, or 3

Q: The diagram shows a stationary 5-kg uniform rod (AC), 1 m long, held against a wall by a rope (AE) and friction between the rod and the wall. To use a single equation to find the force exerted on the rod by the rope at which point should you place the reference point for computing torque? A) A B) B C) C D) D E) E

Q: The ideal mechanical advantage (i.e. the ratio of the weight Wto the pull Pfor equilibrium) of the combination of pulleys shown is: A) 1 B) 2 C) 3 D) 4 E) 5

Q: The pull Pis just sufficient to keep the 14-N block and the weightless pulleys in equilibrium as shown. The tension Tin the upper cable is: A) 14 N B) 28 N C) 16 N D) 9.3 N E) 19 N

Q: A picture is to be hung from the ceiling by means of two wires. Order the following arrangements of the wires according to the tension in wire B, from least to greatest. A) I, II, III B) III, I, II C) I and II tie, then III D) II, I, III E) all tie

Q: A 400-N uniform vertical boom is attached to the ceiling by a hinge, as shown. An 800-N weight Wand a horizontal guy wire are attached to the lower end of the boom as indicated. The pulley is massless and frictionless. The tension force Tof the horizontal guy wire has magnitude: A) 350 N B) 400 N C) 690 N D) 800 N E) 1200 N

Q: A horizontal beam of weight Wis supported by a hinge and cable as shown. The force exerted on the beam by the hinge has a vertical component that must be: A) nonzero and up B) nonzero and down C) nonzero but not enough information given to know whether up or down D) zero E) equal to W

Q: A 960-N block is suspended as shown. The beam AB is weightless and is hinged to the wall at A. The tension force of the cable BC has magnitude: A) 720 N B) 1200 N C) 1280 N D) 1600 N E) none of these

Q: A 240-N weight is hung from two ropes as shown. The tension in the horizontal rope has magnitude: A) 0 N B) 660 N C) 480 N D) 420 N E) 140 N

Q: The 600-N ball shown is suspended on a string AB and rests against the frictionless vertical wall. The string makes an angle of 30ï‚°with the wall. The line AB goes through the center of the ball, and the contact point with the wall is at the same vertical height as the center of the ball. The ball presses against the wall with a force of magnitude: A) 300 N B) 350 N C) 520 N D) 600 N E) 690 N

Q: The 600-N ball shown is suspended on a string AB and rests against the frictionless vertical wall. The string makes an angle of 30ï‚°with the wall. The line AB goes through the center of the ball, and the contact point with the wall is at the same vertical height as the center of the ball. The magnitude of the tension in the string is: A) 300 N B) 520 N C) 690 N D) 1200 N E) none of these

Q: A window washer attempts to lean a ladder against a frictionless wall. He finds that the ladder slips on the ground when it is placed at an angle of less than 75°to the ground but remains in place when the angle is greater than 75°. The coefficient of static friction between the ladder and the ground:A) is 0.13B) is 0.27C) is 1.3D) depends on the mass of the ladderE) depends on the length of the ladder

Q: A uniform ladder is 10 m long and weighs 400 N. It rests with its upper end against a frictionless vertical wall. Its lower end rests on the ground and is prevented from slipping by a peg driven into the ground. The ladder makes a 30°angle with the horizontal. The force exerted on the wall by the ladder is:A) 47 NB) 74 NC) 120 ND) 350 NE) 460 N

Q: An 800-N man stands halfway up a 5.0 m ladder of negligible weight. The base of the ladder is 3.0 m from the wall as shown. Assuming that the wall-ladder contact is frictionless, the wall pushes against the ladder with a force of: A) 150 N B) 300 N C) 400 N D) 600 N E) 800 N

Q: An 80-N uniform plank leans against a frictionless wall as shown. The torque (about point P) applied to the plank by the wall is:A) 40 N.mB) 60 N.mC) 120 N.mD) 160 N.mE) 240 N.m

Q: A ladder leans against a wall. If the ladder is not to slip, which one of the following must be true? A) The coefficient of friction between the ladder and the wall must not be zero B) The coefficient of friction between the ladder and the floor must not be zero C) Both A and B D) Either A or B E) Neither A nor B

Q: A uniform 240-g meter stick can be balanced by a 240-g weight placed at the 100-cm mark if the fulcrum is placed at the point marked: A) 75 cm B) 60 cm C) 50 cm D) 40 cm E) 80 cm

Q: A uniform plank is 6.0 m long and weighs 80 N. It is balanced on a sawhorse at its center. An additional 160 N weight is now placed on the left end of the plank. To keep the plank balanced, it must be moved what distance to the right? A) 6.0 m B) 2.0 m C) 1.5 m D) 1.0 m E) 0.50 m

Q: A 5.0 m weightless strut, hinged to a wall, is used to support an 800-N block as shown. The horizontal and vertical components of the force of the hinge on the strut are: A) FH= 800 N, FY= 800 N B) FH= 600 N, FY= 800 N C) FH= 800 N, FY= 600 N D) FH= 1200 N, FY= 800 N E) FH= 0 N, FY= 800 N

Q: A uniform rod AB is 1.2 m long and weighs 16 N. It is suspended by strings AC and BD as shown. A block P weighing 96 N is attached at E, 0.30 m from A. The magnitude of the tension force in the string BD is: A) 8.0 N B) 24 N C) 32 N D) 48 N E) 80 N

Q: A uniform plank XY is supported by two equal 120-N forces at X and Y, as shown. The support at X is then moved to Z (half-way to the plank center). The supporting forces at Y and Z are then: A) FY= 240 N, FZ= 120 N B) FY= 200 N, FZ= 40 N C) FY= 40 N, FZ= 200 N D) FY= 80 N, FZ= 160 N E) FY= 160 N, FZ= 80 N

Q: A picture can be hung on a wall in three different ways, as shown. The tension in the string is: A) least in I B) greatest in I C) greatest in II D) least in III E) greatest in III

Q: A picture P of weight Wis hung by two strings as shown. The magnitude of the tension force of each string is T. The total upward pull of the strings on the picture is: A) 2Wcosï±ï€ B) Tsin ï±ï€ C) Tcosï±ï€ D) 2Tsin ï±ï€ E) 2Tcosï€

Q: A 160-N child sits on a light swing and is pulled back and held with a horizontal force of 100 N. The magnitude of the tension force of each of the two supporting ropes is: A) 60 N B) 94 N C) 120 N D) 190 N E) 260 N

Q: Three identical uniform rods are each acted on by two or more forces, all perpendicular to the rods. Which of the rods could be in static equilibrium if an additional force is applied at the center of mass of the rod? A) Only 1 B) Only 2 C) Only 3 D) Only 1 and 2 E) All three

Q: A massless meter stick on a horizontal frictionless table top is pivoted at the 80-cm mark. A force is applied perpendicularly to the end of the stick at 0 cm, as shown. A second force (not shown) is applied perpendicularly at the 60-cm mark. The forces are in the plane of the table top. If the stick does not move, the force exerted by the pivot on the stick: A) must be zero B) must be in the same direction as and have magnitude C) must be directed opposite to and have magnitude D) must be in the same direction as and have magnitude E) must be directed opposite to and have magnitude

Q: A massless meter stick on a horizontal frictionless table top is pivoted at the 80-cm mark. A force is applied perpendicularly to the end of the stick at 0 cm, as shown. A second force (not shown) is applied perpendicularly to the stick at the 100-cm end of the stick. The forces are in the plane of the table top. If the stick does not move, the force exerted by the pivot on the stick: A) must be zero B) must be in the same direction as and have magnitude C) must be directed opposite to and have magnitude D) must be in the same direction as and have magnitude E) must be directed opposite to and have magnitude

Q: A 5.1-kg mass is located at the origin, and a 2.3-kg mass is located at x= 4.9 cm. Assuming g is constant, what is the location of the center of mass xcom, and the location of the center of gravity xcog, of the two masses? A) xcom= 1.5 cm, xcog= 3.4 cm B) xcom= 3.4 cm, xcog= 1.5 cm C) xcom= 1.5 cm, xcog= 1.5 cm D) xcom= 3.4 cm, xcog= 3.4 cm E) xcom= 1.5 cm, xcog= 0 cm

Q: A cube balanced with one edge in contact with a table top and with its center of gravity directly above the edge is in ________ equilibrium with respect to rotation about the edge and in ________ equilibrium with respect to rotation about a horizontal axis that is perpendicular to the edge. A) stable, stable B) stable, unstable C) unstable, stable D) unstable, unstable E) unstable, neutral

Q: A cylinder placed so it can roll on a horizontal table top, with its center of gravity below its geometrical center, is: A) in stable equilibrium B) in unstable equilibrium C) in neutral equilibrium D) not in equilibrium E) none of the above

Q: A cylinder placed so it can roll on a horizontal table top, with its center of gravity above its geometrical center, is: A) in stable equilibrium B) in unstable equilibrium C) in neutral equilibrium D) not in equilibrium E) none of the above

Q: The location of which of the following points within an object might depend on the orientation of the object? A) Its center of mass B) Its center of gravity C) Its geometrical center D) Its center of momentum E) None of the above

Q: The center of gravity coincides with the center of mass: A) always B) never C) if the center of mass is at the geometrical center of the body D) if the acceleration due to gravity is uniform over the body E) if the body has a uniform distribution of mass

Q: To determine if a rigid body is in equilibrium the vector sum of the gravitational forces acting on the particles of the body can be replaced by a single force acting at: A) the center of mass B) the geometrical center C) the center of gravity D) a point on the boundary E) none of the above

Q: For a body to be equilibrium under the combined action of several forces: A) all the forces must be applied at the same point B) all of the forces are composed of pairs of equal and opposite forces C) any two of these forces must be balanced by a third force D) the sum of the torques about any point must equal zero E) the lines of action of all the forces must pass through the center of gravity of the body

Q: For a body to be equilibrium under the combined action of several forces: A) all the forces must be applied at the same point B) all of the forces are composed of pairs of equal and opposite forces C) the sum of the components of all the forces in any direction must equal zero D) any two of these forces must be balanced by a third force E) the lines of action of all the forces must pass through the center of gravity of the body

Q: For an object in equilibrium the sum of the torques acting on it vanishes only if each torque is calculated about: A) the center of mass B) the center of gravity C) the geometrical center D) the point of application of the force E) the same point

Q: The conditions that the sum of forces and the sum of the torques both vanish: A) hold for every solid body in equilibrium B) hold only for elastic solid bodies in equilibrium C) hold for every solid body D) are always sufficient to calculate the forces on a solid object in equilibrium E) are sufficient to calculate the forces on a solid object in equilibrium only if the object is elastic

Q: Which of the following is in static equilibrium? A) a rock resting on the ground B) a rock sliding at constant velocity across a frictionless surface C) a rock rotating in place on a frictionless surface D) a rock rotating at a constant rate as it slides at constant velocity across a frictionless surface E) a rock falling off a cliff

Q: Which of the following is NOT in equilibrium? A) a rock resting on the ground B) a rock sliding at constant velocity across a frictionless surface C) a rock rotating in place on a frictionless surface D) a rock rotating at a constant rate as it slides at constant velocity across a frictionless surface E) a rock falling off a cliff

Q: A net torque applied to a rigid object always tends to produce: A) linear acceleration B) rotational equilibrium C) angular acceleration D) rotational inertia E) none of these