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Exam 9: Center of Mass and Linear Momentum

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Question 31

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A hockey puck of mass m traveling along the x axis 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 x axis, 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

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Question 32

Multiple Choice

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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

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Question 33

Multiple Choice

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

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 block moves at 5 m/s in the positive x direction 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 x axis and the incident block has a speed of:

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 2.0-kg block is attached to one end of a spring with a spring constant of 100 N/m and a 4.0-kg block is attached to the other end.The blocks are placed on a horizontal frictionless surface and set into motion.At one instant the 2.0-kg block is observed to be traveling to the right with a speed of 0.50 m/s and the 4.0-kg block is observed to be traveling to the left with a speed of 0.30 m/s.Since the only forces on the blocks are the force of gravity, the normal force of the surface, and the force of the spring, we conclude that:

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:

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:

The acceleration of the center of mass of a system of particles:

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 center of mass of Earth's atmosphere is:

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:

Whenever an object strikes a stationary object of equal mass:

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:

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

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:

Which one of the following statements is true?

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

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: