# Kinetic energy problem

1. Aug 17, 2010

### pokeefer

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

In the 1950's, an experimental train that had a mass of 2.50 x 10 to the power 4 kg was powered accross level track by a jet engine that produced a thrust of 5.00 x 10 to power 5 N for a distance of 500m.

a.) Find the work done by the train

Work = (500,000)(500)
Work is 250,000,000N

b.) Find the change in kinetic energy (1)

c.) Find the final kinetic energy of the train if it started from rest (1)

d.) Find the final speed of the train is there was no friction (2)

2. Relevant equations

Kinetic Energy = 0.5 mv^2

3. The attempt at a solution

So I found out the amount of work required easily but now i'm stuck on b, c, and d.

Since I can't figure out the velocity I can't really use the formula KE = 0.5 mass x velocity squared.

How do I find velocity in this question?

2. Aug 17, 2010

### rock.freak667

The work done by the train is the change in kinetic energy.

3. Aug 17, 2010

### pokeefer

I don't understand.

Work = Force x Distance

kinetic energy is 0.5 mass x velocity squared

How do I use the numbers given to me to figure out velocity so I can figure out kinetic energy?

4. Aug 17, 2010

### rock.freak667

The train is producing a thrust over a certain distance. Within this distance the thrust is essentially increasing the velocity of the train right?

So the work being done by the train is increasing the velocity of the train.

Work done by train = change in kinetic energy.

5. Aug 17, 2010

### pokeefer

Hmmm,

If its increasing the velocity then it must have an acceleration but what would the acceleration be then and how much time did it take for the train to go for that distance?

6. Aug 18, 2010

### rock.freak667

Why would you need all of that for? For general information? I ask since you do not need to find those things to answer the question.

7. Aug 18, 2010

### pokeefer

Alright, if i DONT need to find those things how do i solve for kinetic energy?

8. Aug 18, 2010

### diazona

P.S. On another note, you wrote the wrong units for work in your original post, but that is perhaps not such a big issue.

9. Aug 18, 2010

### pokeefer

how can work = the change in kinetic energy?

Are you saying work, which is 250,000,000N m = ?? Joules (kinetic energy)

Last edited: Aug 18, 2010
10. Aug 18, 2010

### rock.freak667

In order to increase the velocity, the train must do some sort of work.

Also remember that 1 Nm = 1 J

11. Aug 18, 2010

### pokeefer

Alright problem solved.

Thanks for the help.

Last edited: Aug 18, 2010