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fredrick:
When a bullet is fired from a rigidly held rifle, the force exerted by the rifle on the bullet is equal and opposite  to the force  exerted by the bullet on the rifle.

a)explain why the bullet accelerates while the rigidy held rifle does not

b)In most cases when a rifle is fired, the shooter's shoulder moves back as the rifle 'recoils'. If a 4.0 kg rifle fires a 20 g bullet with an initial speed on 300m/s, what is the initial recoil speed of the rifle?

there are no answers to this question( among many others) in the back of the text book?

help

Mao:
a) the two forces @ work are:
rifle on bullet -> large force small mass -> fast acceleration
bullet on rifle -> equal amount of force, but it is acting on a larger mass -> lower acceleration. In this case it is "rigidly held", we can then assume it has some kind of support and the force is transferred...

b) conservation of momentum
assuming the positive direction is the direction of the bullet

dcc:
The speed will be negative because the direction of the recoil is opposite to the direction of the bullet. (which we consider to be the positive direction)

For example, due to conservation of momentum, the momentum after firing should equal 0





Using positive 1.5 would yield a result of 12 N

Mao:

--- Quote from: dcc on January 17, 2008, 03:16:30 pm ---The speed will be negative because the direction of the recoil is opposite to the direction of the bullet. (which we consider to be the positive direction)

For example, due to conservation of momentum, the momentum after firing should equal 0





Using positive 1.5 would yield a result of 12 N


--- End quote ---
yeah... i'm lazy :P

but then that's the thing that seperates 40+ from 30s... *makes major mental note* thnx dcc

fredrick:
Thanks!
And one more:
A doodgem car of mass 200kg is driven due south into a rigid barrier at an initial speed of 5.0m/s. the car rebounds at a speed of 2.0m/s. it is in contact for 0.20 secs. calculate:
a) the average acceleration of the car during its interaction with the barrier.
b) the average net force applied to the car during its interaction with the barrier

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