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Exam 9: Center of Mass and Linear Momentum

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Question 31

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The center of mass of a uniform disk of radius R is located:

A) on the rim
B) a distance R/2 from the center
C) a distance R/3 from the center
D) a distance 2R/3 from the center
E) at the center

F) C) and D)
G) A) and B)

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Question 32

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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

F) B) and E)
G) A) and C)

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Question 33

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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:

The velocity of the center of mass of a system of particles changes as v = 4.5 t + 2.4 t² + 1.1 t³, where v is in meters per second. If the system starts from rest at t = 0, what is its acceleration at t = 3.0 s?

The velocity of the center of mass of a system of particles changes as v = 4.5 t + 2.4 t² + 1.1 t³, where v is in meters per second. If the system starts from rest at t = 0, what is its position at t = 3.0 s?

When you step on the accelerator to increase the speed of your car, the force that accelerates the car is:

A 640-N hunter gets a rope around a 3200-N polar bear. They are stationary, 20 m apart, on frictionless level ice. When the hunter pulls the polar bear to him, the polar bear will move:

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:

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 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 golf ball of mass m is 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 T is:

An elastic collision is one in which:

The center of mass of a system of particles remains at the same place if:

Block A, with a mass of 2.0 kg, moves along the x axis 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 x axis. If B is much more massive than A, the velocity of A after the collision is:

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:

The law of conservation of momentum applies to a system of colliding objects only if:

The direction of the impulse on a struck baseball

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 5-kg object can move along the x axis. It is subjected to a force in the positive x direction; a graph of F as a function of time t is shown below. Over the time the force is applied the change in the velocity of the object is:

At the same instant that a 0.50-kg ball is dropped from 25 m above Earth, a second ball, with a mass of 0.25 kg, is thrown straight upward from Earth's surface with an initial speed of 15 m/s. They move along nearby lines and pass without colliding. At the end of 2.0 s the velocity of the center of mass of the two-ball system is: