Calculating Average Force in a Car Collision

[ScullyX51]

Homework Statement

A 1200 kg car drives headlong into a brick wall at 14 m/s and rebound at 3 m/s. The collision lasts for .10 seconds. What is the average force on the car during the collision?

Homework Equations

F=ma
f*change in time= mass * change in velocity
f= mass*change in velocity / change in time

The Attempt at a Solution

I got the change in velocity to be 17 m/s. I did 14 m/s - (-3m/s) = 17 (I put the 3 as negative since it it rebounding it is going in the negative x direction.
f= 1200(17)/ .1 = 204,000. this is wrong..where am I messing up?

 

[PhanthomJay]

Homework Statement

A 1200 kg car drives headlong into a brick wall at 14 m/s and rebound at 3 m/s. The collision lasts for .10 seconds. What is the average force on the car during the collision?

Homework Equations

F=ma
f*change in time= mass * change in velocity
f= mass*change in velocity / change in time

The Attempt at a Solution

I got the change in velocity to be 17 m/s. I did 14 m/s - (-3m/s) = 17 (I put the 3 as negative since it it rebounding it is going in the negative x direction.
f= 1200(17)/ .1 = 204,000. this is wrong..where am I messing up?

The change in velocity is (final v - initial v). You may have a signage error. And don't forget the force unit.

 

[borgwal]

Looks good to me, except for you not including the correct unit for force.