# Homework Help: What average force is it brought to rest?

1. Nov 17, 2007

### missashley

1. The problem statement, all variables and given/known data

Auto companies frequently test the safety of automobiles by putting them through crash tests to observe the integrity of the passenger compartment. If a 1000. kg car is sent toward a cement wall with a speed of 14 m/s and the impact brings it to a stop in 8.00 * 10^-2 seconds, with what average force is it brought to rest?

2. Relevant equations

F = mv/t

3. The attempt at a solution

F = mv/t = (1000*14)/(8e-2) = 175000 N

2. Nov 17, 2007

### dynamicsolo

There you have it! The average acceleration during the simulated crash is the change in velocity (14 - 0 m/sec) divided by the time interval over which it occurred (0.08 sec) or 175 m/(sec^2) , which is almost 18 times the acceleration of gravity. The average force on the car is then its mass times that average acceleration or

175 m/(sec^2) ยท 1000 kg = 175,000 N (or almost 18 times the car's weight).

3. Nov 18, 2007

Thats right.