(see page 107 of the text).ġ7) If the box of the previous question is dropped, its K.E. See page 61).ġ6) If the box of the previous question is raised to a height of 1.5 meters, its potential energy is If the box is displaced by 6 meters, the amount of work done on the box is The others are all smaller than this number.ġ5) A 100-kg box is pushed with a force of 35 lb. Thus the long cannon produces a larger momentum.ġ4) Which of the following objects has the largest kinetic energy? To increase the momentum of the outgoing shell, the time of contact must increase. The momentum is independent of the length of the cannon
Why?Ī) Momentum is not conserved in this case, and as a result the tube does not recoil.ī) Momentum is shared between the gas and the shell the tube does not recoil.Ĭ) Since the tube is held on the shoulder, its mass is high and it does not recoil.ĭ) There is a significant recoil it is absorbed by the large mass of the tube.ġ2) In order to reduce the "sting" in catching ahard ball one usually,ġ3) For the same force, which one imparts a greater momentumto a cannonball?Ĭ) either (a) or (b) depending on the air resistanceĭ) neither (a) nor (b).
There is a very little recoil on the person firingthe shell. This is doneĪ) so they can replace them every year and provide jobs for unemployed workersī) so the cars cannot rebound back to the middle of the roadĬ) to increase the contact time and decrease the crash forceĭ) to increase the momentum and decrease the crash forceġ1) A bazooka, or rocket launcher, is essentially a large tube,open at both ends, that a soldier holds on the shoulder when firinga heavy shell. Reasoning: Using the relationship between force and momentum (discussed on question 7 and on page 89 of the text), as the time of contact increases the force will decrease.ġ0) Guardrails along roadsides collapse (bend and crumple)when a car runs into them. What does thishead motion accomplish?Ī) It increases the momentum and decreases the forceī) It increases the contact time which decreases the forceĬ) It decreases the contact time which decreases the force Using F = change in momentum/contact time, we get: F = (.2 kg x 30 m/s)/(.1 s) = 60 N.ĩ) A boxer quickly learns to move his head backward when hesees he is going to receive a jab to the head. The ball comes to rest in about 1/10 second.The force acting on the players hand is (Think of the relationshipbetween change of the momentum and force), Reasoning: Use the conservation of momentum law.Study the examples on page 96-97 of the text.ħ) A baseball player grabs a 200 gram baseball which is movingat speed of 30 m/s. Their speed immediatelyafter the collision is Thus if two objects have the same momentum, the lighter object will have a larger velocity.Ħ) A 1500 kg truck traveling at 80 km/h collides with anothercar of mass 1000 kg traveling at 30 km/h in the same direction.The two cars stick together after the collision. Reasoning: If you throw the books forward (!), then you will suffer a backward momentum because of the law of conservation of momentum.Ģ) A heavy truck has more momentum than a passenger car movingat the same speed because the truckī) in an inelastic collision of two ballsĤ) A gun recoiling when it is fired is an example ofĥ) A heavy object and a light object have the same momentum.Which has the greater speed?ĭ) the heavy object has a zero speed while the light object has a nonzero speed As you are about to fall, you suddenly remember how physicscan save you! What law did you remember?
1) Suppose you find yourself teetering on the edge of a cliffor the roof of a tall building with a heavy physics book in yourhand.
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