Physics-momentum/impluse

posted by becky

hi

well i have two questions i don't understand how to solve and all.

1) The front of a 1400-kg car is designed to absorb the shock of a collision by having a "crumple zone" in which the front of 1.2m of the car collapses in absorbing the shock of a collision. if a car traveling 25.0m/s stops uniformly in 1.2m, (a)how long does the collision last, (b) what is the magnitude of the average force on the car, and (c) what is the acceleration of the car in g's?

2) A 0.15kg baseball is thrown with a speed of 20m.s It is hit straight back at the pitcher with a final speed of 22m/s. (a) what is the impulse delivered to the ball? (b) find the average forece exerted by the bat on the ball if the two are in contact for 2.0 X 10^-3 seconds.

Thanks in advance..i really don't understand these two problems

a) To decelerate from velocity V to zero in a distance X, you need acceleration rate a given by
a = V^2/2X. The time to decelerate it
T = V/a = 2X/V

b)F = M a

c) divide a = V2/(2X) by g = 9.8 m/s^2 for the acceleration in g's.

2) (a) Use the fact that the momentum change equals the impulse. Consider the change of sign of the velocity when calculating the momentum change.
(b) Average force = (Impulse)/(time force is applied0

ohh i get it! thanks

wait umm for the second one... i don't understand ..like i know the process but yet its not working out for me..

for instance for part a) i don't understand like how to get it..i mean i know you would do FT=MV and then i don't know what exactly is to be done with..

b) ummm impulse/time..so it would be .15(2)/2.0*10^-3..but then it doesnt come out to the answer in the back of the book..

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