# Physics Practice Work For Chapters 6 & 7

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question
(Reading 6.10) Which has a greater momentum: a heavy truck at rest or a moving skateboard?
The moving skateboard
question
For the same force, why does a long cannon impart more speed to a cannonball than a short cannon?
The force is applied for a longer time in the long cannon
question
How is the impulse -momentum relationship related to Newton's second law?
F=ma=mΞv/Ξt, so Ft=Ξ(mv)
question
When you are struck by a moving object, is it favorable that the object makes contact with you over a short time or over a long time?
Long contact time decreases the magnitude of the average force and is favorable
question
Why is a force that is applied for a short time more effective in karate
The average force is increased. (A force that is applied for a short time is able to deliver a high impact force for the same change in momentum).( if the time is small the force will be greater Ft=mv)
question
Why is it advantageous to roll with the punch in boxing
Rolling with the punch increases contact time, which decreases the force.
question
When a cannonball is fired, the momentum of the system (cannon + cannonball) is conserved if
the momentum of the cannon is equal to the magnitude of the momentum of the cannon ball and points in the opposite direction
question
When a big fish swims into an oncoming smaller fish and swallows it, the momentum of the two-fish system ______
remains the same
question
In which is momentum conserved: an elastic collision or an inelastic collision
Momentum is conserved in elastic and inelastic collisions
question
A freight train rolls along a track with considerable momentum. If it rolls at the same speed but has twice as much mass, its momentum is