Conceptual Questions
9.1 Linear Momentum
An object that has a small mass and an object that has a large mass have the same momentum. Which object has the largest kinetic energy?
An object that has a small mass and an object that has a large mass have the same kinetic energy. Which mass has the largest momentum?
9.2 Impulse and Collisions
Is it possible for a small force to produce a larger impulse on a given object than a large force? Explain.
Why is a 10-m fall onto concrete far more dangerous than a 10-m fall onto water?
What external force is responsible for changing the momentum of a car moving along a horizontal road?
A piece of putty and a tennis ball with the same mass are thrown against a wall with the same velocity. Which object experiences a greater force from the wall or are the forces equal? Explain.
9.3 Conservation of Linear Momentum
Can momentum be conserved for a system if there are external forces acting on the system? If so, under what conditions? If not, why not?
Explain in terms of momentum and Newton’s laws how a car’s air resistance is due in part to the fact that it pushes air in its direction of motion.
Can objects in a system have momentum while the momentum of the system is zero? Explain your answer.
A sprinter accelerates out of the starting blocks. Can you consider him as a closed system? Explain.
A rocket in deep space (zero gravity) accelerates by firing hot gas out of its thrusters. Does the rocket constitute a closed system? Explain.
9.4 Types of Collisions
Two objects of equal mass are moving with equal and opposite velocities when they collide. Can all the kinetic energy be lost in the collision?
Describe a system for which momentum is conserved but mechanical energy is not. Now the reverse: Describe a system for which kinetic energy is conserved but momentum is not.
9.5 Collisions in Multiple Dimensions
Momentum for a system can be conserved in one direction while not being conserved in another. What is the angle between the directions? Give an example.
9.6 Center of Mass
Suppose a fireworks shell explodes, breaking into three large pieces for which air resistance is negligible. How does the explosion affect the motion of the center of mass? How would it be affected if the pieces experienced significantly more air resistance than the intact shell?
9.7 Rocket Propulsion
It is possible for the velocity of a rocket to be greater than the exhaust velocity of the gases it ejects. When that is the case, the gas velocity and gas momentum are in the same direction as that of the rocket. How is the rocket still able to obtain thrust by ejecting the gases?