# Kinetic Energy and mass

1. Nov 30, 2015

### Marts12

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

A) A car moving at 18 m/s is accelerated to 35 m/s. If the change in kinetic energy is 154 kJ, determine the mass of the car.

2. Relevant equations

KE = 0.5mv^2
Kinetic energy = change in momentum = mv2-mv1

3. The attempt at a solution

Im not sure how to go about this problem, but I suspect that the mass can be obtained from the fact that kinetic energy is equal to the change in momentum?

2. Nov 30, 2015

### Staff: Mentor

Aren't these two equations contradictory? Which one is correct?

3. Dec 1, 2015

### Marts12

KE=0.5mv^2 is the correct equation for kinetic energy, but we are given that.

Am I right in saying that I need an equation that relates the change in Kinetic energy to mass?

4. Dec 1, 2015

### Staff: Mentor

Yes, and you already have all the ingredients to construct that equation yourself.

5. Dec 1, 2015

### Marts12

Ok,

If I were to say that Change in Kinetic Energy = mv2^2 - mv1^2

Where v2 = final velocity and
V1 = initial velocity

Would I be on the right lines?

6. Dec 1, 2015

### haruspex

Nearly, but you lost the 1/2.

7. Dec 1, 2015

### Marts12

Perfect so,

Change in Kinetic Energy = 0.5mv2^2 - 0.5mv1^2

Thank you for your help DrClaude