# physics review help

Discussion in 'Physics' started by xt3rmin8, Jul 6, 2009.

1. ### xt3rmin8 Thread Starter New Member

Sep 1, 2008
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1)A 1.2kb object moving with a speed of 8m/s collides perpendicularly with a wall and emergences with a speed of 6 m/s in the opposite direction. If the object is in contact with the wall for 2.0 ms, what is the magnitude of the average force on the object by the wall?

2)at what rate is the gravitational force on a 2kg projectile doing work at an instant when the velocity of the projectile is 4 m/s directed 30° above the horizontal?

3 A 2kg object moving with a velocity of 5m/s is in the positive x direction strikes and sticks to a 3 kg object moving with a speed of 2 m/s in the same direction. how much kinetic energy is lost in the collision?

thanks

Jul 7, 2009
1,585
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1) Calculate the change in momentum and use the fact that the impulse is equal to the momentum change.

2) Hint: work is the rate of change of energy, so look at the rate of change of energy in the direction antiparallel to the gravitational force vector.

3) Calculate the kinetic energies before and after the collision. Remember kinetic and potential energies aren't conserved in inelastic collisions (but momentum is).

3. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
513
More fully, since you are asked for the force and given the time, use the fact that the impulse

I = ∫Fdt = change in momentum.