Exam 9: Center of Mass and Linear Momentum

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:

A projectile in flight explodes into several fragments.The total momentum of the fragments immediately after this explosion:

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 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:

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

The thrust of a rocket is

A large wedge with a mass of 10 kg rests on a horizontal frictionless surface, as shown.A block with a mass of 5.0 kg starts from rest and slides down the inclined surface of the wedge, which is rough.At one instant the vertical component of the block's velocity is 3.0 m/s and the horizontal component is 6.0 m/s.At that instant the velocity of the wedge 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 acceleration of the center of mass of the two-ball system is:

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 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:

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 each other without colliding.At the end of 2.0 s the height above Earth's surface of the center of mass of the two-ball system is:

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:

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 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 momentum of an object at a given instant is in the same direction as its:

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:

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:

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:

Blocks A and B are moving toward each other along the x axis.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 x axis.The kinetic energy transferred from A to B during the collision is:

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: