# Homework Help: Work and Energy

1. Nov 17, 2015

### Chris18

1. The problem statement, all variables and given/known data
Hey guys. I have a problem to solve but I am stacked and I don't now how,so any help will be hghly appreciated.The problem is the following: A truck of mass 9000kg is moving with speed 18m/s, when the driver decides to stop and applies the brakes. After 6s the truck stops. Assuming that the stopping is with constant deceleration calculate the followin:

a)The distance traveled by the car during stopping
b)The acceleration of the truck
c)The loss of energy due to friction

I would be grateful if you can give me some ideas using energy mostly but I wouldn't mind if you tell me another way through Newton Laws e.t.c!!!

2. Relevant equations

3. The attempt at a solution
So I personally started (a) by finding the acceleration through Newton's Second law a=F/m...Then I used v^2/2a to define the distance travelled (S).....So i found the acceleration in question (a) so (b) is ready as well i think..I don't know what to do in (c) though

2. Nov 17, 2015

### Krikor Hagopian

d = -(speed)^2/(2*deceleration)
is the minimum distance travelled

3. Nov 17, 2015

### Staff: Mentor

Tell us what you know about how work is calculated, and about the work-energy theorem.

Chet

4. Nov 17, 2015

### Chris18

Well work is calculated by W=F*d*cos(θ). I know the basics of the work-energy theorem. Still I can't understand how to solve part (c) of the problem...

5. Nov 17, 2015

### Staff: Mentor

What is the change in kinetic energy of the truck?

Chet

6. Nov 19, 2015

### Chris18

My idea is to use the equation of kinetic energy since the loss of energy must be equal to the initial kinetic energy of the truck according to law of conservation! Tell me if I am wrong pls!! Best regards.