How Do You Calculate Car Mass from Kinetic Energy Change?

[Marts12]

Homework Statement

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.

Homework Equations

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

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?

 

[DrClaude]

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

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

 

[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?

 

[DrClaude]

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?

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

 

[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?

 

[haruspex]

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?

Nearly, but you lost the 1/2.

 

[Marts12]

Perfect so,

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

Thank you for your help DrClaude