PHY 2053 EXAM 2

On a balanced seesaw, a boy three times as heavy as his partner sits A) 1/3 the distance from the fulcrum. B) less than 1/3 the distance from the fulcrum. C) more than 1/3 the distance from the fulcrum.

A) 1/3 the distance from the fulcrum.

A rubber ball and a lump of clay have equal mass. They are thrown with equal speed against a wall. The ball bounces back with nearly the same speed with which it hit. The clay sticks to the wall. Which one of these objects experiences the greater momentum change? A) the ball B) the clay C) Both of them experience the same non-zero momentum change. D) Both of them experience zero momentum change.

A) The Ball

Which of the following statements is correct? A) The ratio of tensile stress to tensile strain is called Young's modulus. B) "Strain" has a meaning very close to "force." C) "Stress" has a meaning very close to "stretch." D) Tensile stress is measured in newtons. E) Tensile strain is measured in meters.

A) The ratio of tensile stress to tensile strain is called Young's modulus.

Three cars, car X, car Y, and car Z, begin accelerating from rest at the same time. Car X is more massive than car Y, which is more massive than car Z. The net accelerating force exerted on each car is identical. After 10 seconds, which car has the most amount of momentum? A) They all have the same amount of momentum. B) Car X C) Car Y D) Car Z

A) They all have the same amount of momentum

When a rigid object rotates about a fixed axis, what is true about all the points in the object? (There could be more than one correct choice.) A) They all have the same angular speed. B) They all have the same tangential speed. C) They all have the same angular acceleration. D) They all have the same tangential acceleration. E) They all have the same radial acceleration.

A) They all have the same angular speed. C) They all have the same angular acceleration.

The famous Leaning Tower of Pisa doesn't topple over because its center of gravity is A) above a place of support. B) relatively low for such a tall building. C) stabilized by its structure. D) displaced from its center. E) in the same place as its center of mass.

A) above a place of support.

A 10-kg piece of aluminum sits at the bottom of a lake, right next to a 10-kg piece of lead, which is much denser than aluminum. Which one has the greater buoyant force on it? A) the aluminum B) the lead C) Both have the same buoyant force. D) It cannot be determined without knowing their volumes

A) the aluminum

Two equal-magnitude forces are applied to a door at the doorknob. The first force is applied perpendicular to the door, and the second force is applied at 30° to the plane of the door. Which force exerts the greater torque about the door hinge? A) the first force (applied perpendicular to the door) B) the second force (applied at an angle) C) Both forces exert equal non-zero torques. D) Both forces exert zero torque.

A) the first force (applied perpendicular to the door)

Two forces produce equal torques on a door about the door hinge. The first force is applied at the midpoint of the door; the second force is applied at the doorknob. Both forces are applied perpendicular to the door. Which force has a greater magnitude? A) the first force (at the midpoint) B) the second force (at the doorknob) C) The two forces are equal.

A) the first force (at the midpoint)

Tensile strain is A) the ratio of the change in length to the original length. B) the stress per unit area. C) the applied force per unit area. D) the ratio of stress to elastic modulus.

A) the ratio of the change in length to the original length.

If you stood on a planet having a mass four times that of Earth's mass, and a radius two times that of Earth's radius, you would weigh A) the same as you do on Earth. B) two times more than you do on Earth. C) two times less than you do on Earth. D) four times more than you do on Earth.

A) the same as you do on Earth.

Suppose our sun had 4 times its present mass but the earth orbited it at the same distance as it presently does. What would be the length of the year on the earth under those conditions? A) 1/4 as long as the present year B) 1/2 as long as the present year C) the same as the present year D) twice as long as the present year E) four times as long as the present year

B) 1/2 as long as the present year

Two small objects, with masses m and M, are originally a distance r apart, and the magnitude of the gravitational force on each one is F. The masses are changed to 2m and 2M, and the distance is changed to 4r. What is the magnitude of the new gravitational force? A) F/16 B) F/4 C) 16F D) 4F E) F/2

B) F/4

If the sum of both the external torques and the external forces on an object is zero, then the object must be at rest. A) True B) False

B) False

There must be equal amounts of mass on both sides of the center of mass (or center of gravity) of a system. A) True B) False

B) False

Two children, Ahmed and Jacques, ride on a merry-go-round. Ahmed is at a greater distance from the axis of rotation than Jacques. Which of the following are true statements? (There could be more than one correct choice.) A) Jacques has a greater angular speed than Ahmed. B) Jacques and Ahmed have the same angular speed. C) Jacques has a smaller angular speed than Ahmed. D) Ahmed has a greater tangential speed than Jacques. E) Jacques and Ahmed have the same tangential speed.

B) Jacques and Ahmed have the same angular speed. D) Ahmed has a greater tangential speed than Jacques.

10) A very elastic rubber ball is dropped from a certain height and hits the floor with a downward speed v. Since it is so elastic, the ball bounces back with the same speed v going upward. Which of the following statements about the bounce are correct? (There could be more than one correct choice.) A)The ball had the same momentum just before and just after the bounce. B) The magnitude of the ball's momentum was the same just before and just after the bounce. C) None of the above statements are correct

B) The magnitude of the ball's momentum was the same just before and just after the bounce.

A coin and a ring of a similar dimension roll down an incline starting at the same time. The one to reach the bottom first will be the A) ring. B) coin. C) Both reach the bottom at the same time.

B) coin.

A boat loaded with rocks is floating in a swimming pool. If the rocks are thrown into the pool, the water level in the pool, after the rocks have settled to the bottom, A) rises. B) falls. C) stays the same.

B) falls.

Salt water is denser than fresh water. A ship floats in both fresh water and salt water. Compared to the fresh water, the volume of water displaced in the salt water is A) more. B) less. C) the same. D) Cannot be determined because we do not know the volume of the ship.

B) less.

Horses that move with the fastest linear speed on a merry-go-round are located A) near the center. B) near the outside. C) anywhere, because they all move at the same speed.

B) near the outside.

When you blow some air above a paper strip, the paper rises. This happens because A) the air above the paper moves faster and the pressure is higher. B) the air above the paper moves faster and the pressure is lower. C) the air above the paper moves faster and the pressure remains constant. D) the air above the paper moves slower and the pressure is higher. E) the air above the paper moves slower and the pressure is lower.

B) the air above the paper moves faster and the pressure is lower.

The reason an astronaut in an earth satellite feels weightless is that A) the astronaut is beyond the range of the earth's gravity. B) the astronaut is freely falling. C) the astronaut is at a point in space where the effects of the moon's gravity and the earth's gravity cancel. D) this is a psychological effect associated with rapid motion. E) the astronaut's acceleration is zero.

B) the astronaut is freely falling.

When a car goes around a circular curve on a horizontal road at constant speed, what force causes it to follow the circular path? A) the normal force from the road B) the friction force from the road C) gravity D) No force causes the car to do this because the car is traveling at constant speed and therefore has no acceleration.

B) the friction force from the road

In a real collision, A. kinetic energy is conserved. B. linear momentum is conserved in the absence of external forces. C. both momentum and kinetic energy are conserved. D. neither momentum nor kinetic energy is conserved. E. the extent to which momentum and kinetic energy are conserved depends on the coefficient of restitution.

B. linear momentum is conserved in the absence of external forces.

A tiger is running in a straight line. If we double both the mass and speed of the tiger, the magnitude of its momentum will increase by what factor? A) B) 2 C) 4 D) 8 E) 16

C) 4

Two bocks of wood float in water in such a way that the second block of wood sits on top of the first block. Now, if the top piece is taken off and placed in the water and if both the pieces float independently, what happens to the water level in the tub? A) It goes up. B) It goes down. C) It does not change. D) It cannot be determined without knowing the volumes of the two pieces of wood.

C) It does not change.

As a rock sinks deeper and deeper into water of constant density, what happens to the buoyant force on it if it started above the surface of the water? A) The buoyant force keeps increasing steadily. B) The buoyant force remains constant. C) The buoyant force first increases and then remains constant. D) The buoyant force steadily decreases.

C) The buoyant force first increases and then remains constant.

When an object moves in uniform circular motion, the direction of its acceleration is A) in the same direction as its velocity vector. B) in the opposite direction of its velocity vector. C) is directed toward the center of its circular path. D) is directed away from the center of its circular path. E) depends on the speed of the object.

C) is directed toward the center of its circular path.

Which of the following quantities are units of impulse? (There could be more than one correct choice.) A) N · m B) kg · s/m C) kg · m/s D) N · s E) kg · m2/s2

C) kg · m/s D) N · s

A wooden block contains some nails so that its density is exactly equal to that of water. If it is placed in a tank of water and released from rest when it is completely submerged, it will A) rise to the surface. B) sink to the bottom. C) remain where it is released.

C) remain where it is released.

A ring, a disk, and a solid sphere begin rolling down a hill together. The one to reach the bottom first is the A) ring. B) disk. C) sphere. D) They all reach the bottom at the same time. E) Not enough information is given.

C) sphere.

18) The condition necessary for the conservation of linear momentum in a given system is that A. energy is conserved. B. one body is at rest. C. the net external force is zero. D. internal forces equal external forces. E. none of these is correct.

C. the net external force is zero.

The acceleration due to gravity on Planet A is one-sixth what it is on Planet B, and the radius of the Planet A is one-fourth that of Planet B. The mass of Planet A is what fraction of the mass of Planet B? A) 1/6 B) 1/16 C) 1/24 D) 1/96 E) 1/12

D) 1/96

Two small objects, with masses m and M, are originally a distance r apart, and the gravitational force on each one has magnitude F. The second object has its mass changed to 2M, and the distance is changed to r/4. What is the magnitude of the new gravitational force? A) F/32 B) F/16 C) 16F D) 32F E) 2F

D) 32F

Two small balls, A and B, attract each other gravitationally with a force of magnitude F. If we now double both masses and the separation of the balls, what will now be the magnitude of the attractive force on each one? A) 16F B) 8F C) 4F D) F E) F/4

D) F

A spaceship is traveling to the Moon. At what point is it beyond the pull of Earth's gravity? A) when it gets above the atmosphere B) when it is half-way there C) when it is closer to the Moon than it is to Earth D) It is never beyond the pull of Earth's gravity.

D) It is never beyond the pull of Earth's gravity.

Satellite A has twice the mass of satellite B, and moves at the same orbital distance from Earth as satellite B. Compare the speeds of the two satellites. A) The speed of B is twice the speed of A. B) The speed of B is one-half the speed of A. C) The speed of B is one-fourth the speed of A. D) The speed of B is equal to the speed of A. E) The speed of B is four times the speed of A.

D) The speed of B is equal to the speed of A.

Tensile stress is A) the strain per unit length. B) the same as force. C) the ratio of the change in length. D) applied force per cross-sectional area.

D) applied force per cross-sectional area.

A hypothetical planet has a mass of one-half that of the earth and a radius of twice that of the earth. What is the acceleration due to gravity on the planet in terms of g, the acceleration due to gravity at the surface of the earth? A) g B) g/2 C) g/4 D) g/8 E) g/16

D) g/8

A person sits on a freely spinning lab stool that has no friction in its axle. When this person extends her arms, A) her moment of inertia decreases and her angular speed increases. B) her moment of inertia decreases and her angular speed decreases. C) her moment of inertia increases and her angular speed increases. D) her moment of inertia increases and her angular speed decreases. E) her moment of inertia increases and her angular speed remains the same.

D) her moment of inertia increases and her angular speed decreases.

Momentum is conserved in which of the following? A. elastic collisions B. inelastic collisions C. explosions D. All of these are correct.

D. All of these are correct.

Two identical bodies of mass M move with equal speeds v. The direction of their velocities is illustrated above. The magnitude of the linear momentum of the system is A. 2Mv. B. Mv. C. 4Mv. D. Mv. E. Mv.

D. Mv.

A bullet of mass m and velocity strikes and becomes imbedded in a wooden block of mass M, which is initially at rest on a frictionless surface. The ratio of the velocity of the system after collision to the initial velocity of the bullet is A. (M + m)/m B. (M + m)/M C. M/(m + M) D. m/(m + M) E. M/(m - M)

D. m/(m + M)

Planet A has twice the mass of Planet B. From this information, what can we conclude about the acceleration due to gravity at the surface of Planet A compared to that at the surface of Planet B? A) The acceleration due to gravity on Planet A must be twice as great as the acceleration due to gravity on Planet B. B) The acceleration due to gravity on Planet A must be four times as great as the acceleration due to gravity on Planet B. C) The acceleration due to gravity on Planet A is the same as the acceleration due to gravity on Planet B. D) The acceleration due to gravity on Planet A is greater than the acceleration due to gravity on Planet B, but we cannot say how much greater. E) We cannot conclude anything about the acceleration due to gravity on Planet A without knowing the radii of the two planets.

E) We cannot conclude anything about the acceleration due to gravity on Planet A without knowing the radii of the two planets.

A satellite encircles Mars at a distance above its surface equal to 3 times the radius of Mars. If gm is the acceleration due to gravity at the surface of Mars, what is the acceleration due to gravity at the location of the satellite? A) gm/9 B) 0 C) gm D) gm/3 E) gm/16

E) gm/16

Consider a brick that is totally immersed in water, with the long edge of the brick vertical. The pressure on the brick is A) the same on all surfaces of the brick. B) greatest on the face with largest area. C) greatest on the top of the brick. D) greatest on the sides of the brick. E) greatest on the bottom of the brick.

E) greatest on the bottom of the brick.

For a system consisting of two particles that undergo an elastic collision, A. momentum is conserved but the total energy is not conserved. B. neither the kinetic energy nor the momentum is conserved. C. neither the total energy nor the momentum is necessarily conserved. D. the mechanical energy is conserved but momentum is not conserved. E. both kinetic energy and momentum are conserved.

E. both kinetic energy and momentum are conserved.

Two equal masses travel in opposite directions with equal speeds. They collide in a collision that is between elastic and inelastic. Just after the collision, their velocities are A. zero. B. equal to their original velocities. C. equal in magnitude but opposite in direction to their original velocities. D. less in magnitude and in the same direction as their original velocities. E. less in magnitude and opposite in direction to their original velocities.

E. less in magnitude and opposite in direction to their original velocities.