# Homework Help: Conservation of Energy HW HELP

1. Nov 30, 2013

### HopelessMe

1. A car of mass 800kg is at rest. The engine exerts a resultant force of 2000 N for a distance of 5m. a) What is then its kinetic energy? b) What is then its speed?

2. It is required that you must not use any SUVAT equations while solving this problem.

Possible equations to use are:
kinetic energy = 1/2 x m x v^2
Gravitational Potential Energy = m x g x h
Work = force x distance
F = m x a
W = m x g

3. I have attempted this question a number of times as I'm trying to find the velocity, but since there is no height in this question, I can't use the GPE equation, I'm just a little bit confused and would really appreciate some help.

2. Nov 30, 2013

### tiny-tim

Hi HopelessMe! Welcome to PF!

Try work = force x distance.

(btw, strictly, it's force "dot" displacement)

3. Nov 30, 2013

### HopelessMe

Force x distance = 2000 N x 5 m = 10000 J

Okay, how do I use 10 000 J :shy:

4. Nov 30, 2013

### tiny-tim

Do you know the work energy theorem?

5. Nov 30, 2013

### HopelessMe

Hey Tiny-Tim,

I don't believe I'm aware of the theorem. I know that work is the energy that's been changed from one form to another...

6. Nov 30, 2013

### HopelessMe

So do you mean to say that the work done is equal to the kinetic energy?

7. Nov 30, 2013

### tiny-tim

work done equals the increase in mechanical energy …

that's kinetic energy plus various forms of potential energy​