What force is applied to the car?

Question

At a race track, a car of mass 1150 kg crashes into a concrete wall at a speed of 85 m/s.

 

a. The car crashes into the wall, stopping in 0.1 seconds. What force is applied to the car?

 

(I'm not sure about the formulas for this question. I thought maybe is was the stopping distance equation but that doesn't seem right because I'm trying to figure out the force.)

 

b. The race track installs barrels of sand along the wall. They want to reduce the force on a 1150 kg car crashing at 85 m/s to 200,000 N. By what factor must the barrels increase the time of the crash?

Answer 1

Karlee,

This is a momentum / impulse question.   Δp = F•(Δt)

The momentum of the car goes from 1150*85 = 97750 to 0 in 0.1 seconds.

From this we get the equation 97750 = F(.1)

                                             a)   F = 977500 N

For part b), the change in momentum is unchanged, so we must increase the time in order to decrease the force.

                                          97750 = 200000(t)

                                       b)       t = 0.49 s  or .5 s considering sig figs which means an increase factor of 5

 

Hope that helps.