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Please help! I have a test tomorrow.

A car with a weight of 15,000 N moves horizontally at 30 m/s.

a) What is the car's KE?

b) What will be the magnitude friction force to stop the car over a 60m distance?

F=ma

KE=1/2*m*v

a) mass of car = 1531 kg

KE = 1/2(1531)(30)

b) This is where I hit trouble.

I found acceleration by (0-30)/2 = -15 m/s

Then I used F=ma, so F

Not the correct answer...

1. Homework Statement1. Homework Statement

A car with a weight of 15,000 N moves horizontally at 30 m/s.

a) What is the car's KE?

b) What will be the magnitude friction force to stop the car over a 60m distance?

## Homework Equations

F=ma

KE=1/2*m*v

^{2}## The Attempt at a Solution

a) mass of car = 1531 kg

KE = 1/2(1531)(30)

^{2}= 690,000 Jb) This is where I hit trouble.

I found acceleration by (0-30)/2 = -15 m/s

^{2}Then I used F=ma, so F

_{f}= (1531)(-15) = -22,965 NNot the correct answer...

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