2.4 Momentum

Two carts of different mass m and M are connected by a spring. They are pushed together such that the spring is compressed.

After the carts are released, the cart of mass m moves with velocity v. The change in the momentum of mass M is

• mv

• -mv

• Mv

• -Mv

The momentum of a system is conserved if

• no external forces act on the system

• no friction forces act within the system

• no kinetic energy is lost or gained by the system

• the forces acting on the system are in equilibrium

A body is moving in a straight line. A force F acts on the body in the direction of the body's motion. A resistive force f acts on the body. Both forces act along the same straight line as the motion of the body. The rate of change of momentum of the body is equal to

• F - f

• F

• F + f

• f

The momentum of an object changes by  $\Delta p$  in a time  $\Delta t$  . What is the impulse acting on the object during this change?

•  $\Delta p$  

•  $\Delta p\ \Delta t$  

•  $\frac{\Delta p}{\Delta t}$  

• zero

A ball of mass 0.40 kg travels horizontally and strikes a vertical wall with a speed of 5.0 m s^-1. It rebounds horizontally with a speed of 3.0 m s^-1. The ball is in contact with the wall for a time of 0.20 s.

What is the average magnitude of the force exerted by the ball on the wall?

• 0.16 N

• 0.64 N

• 4 N

• 16 N

In the collision between two bodies, Newton's third law

• only applies if momentum is conserved in the collision

• only applies if energy is conserved in the collision

• only applies if both momentum and energy are conserved in the collision

• always applies

Two identical spheres, each of mass m and speed v, travel towards each other on a frictionless surface in a vacuum.

The spheres undergo a head-on collision.

Which statement correctly describes the spheres after the collision?

• The total momentum of the spheres is 2mv

• Each sphere has zero momentum

• The total kinetic energy of the spheres is mv²

• Each sphere has zero kinetic energy

A rocket is fired vertically into the air. When the rocket reaches its maximum height, the rocket explodes.

What change, if any, occurs in the momentum and in the kinetic energy of the rocket during the explosion?

• p increases and KE increases

• p increases and KE constant

• p constant and KE increases

• p constant and KE constant

A net force of magnitude F acts on a body for a time  $\Delta t$  producing an impulse of magnitude Y. 
Which of the following is the magnitude of the rate of change of momentum of the body?

• F

• F $\Delta t$  

•  $Y\Delta t$  

An object of mass m is initially at rest. An impulse I acts on the object. The change in KE of the object is

• $\frac{I^2}{2m}$

• $\frac{I^2}{m}$

• $I^2m$

• $2I^2m$