# Homework Help: Conservation of engery and work 2.

1. Apr 11, 2012

### Ereny

ben carries a 200N suitcase up three flights of stairs total vertical distance of 10.0m and then pushes the suitcase with a horizontal force of 50.0 N at a constant speed of 50 m s for a horizontal of 35.0 m across the 3rd floor how much work does Ben do on the suitcase during this entire motion

Total work done by Ben = mgh + F*s = 200 * 10 + 50 *35 = 2000 + 1750 = 3750 Joules.

i have a feeling this is wrong i really need help!!

2. Apr 11, 2012

### Staff: Mentor

That's close. You left out the acceleration of gravity when you plugged in the numbers.

It helps to carry units along in your equations -- if you had, you would have noticed that the units were not Joules when you calculated just mh instead of mgh.

Try again (with units this time)?

3. Apr 11, 2012

### Ereny

yeah well 200 n includes the 9.81 so i dont need to include it again right?

4. Apr 11, 2012

### Staff: Mentor

Whoops! You are right!

5. Apr 11, 2012

### Ereny

okay so heres what i did

200N x 10m + 50 N x .5om/s = 2025

Last edited by a moderator: Apr 11, 2012
6. Apr 11, 2012

### Ereny

and i think i typed the velocity wrong in the question is should be .50 m/s

7. Apr 11, 2012

### Staff: Mentor

No, you had it right the first time. When pushing the object, the work is force X distance. The units of work are Newtons * meters, not Nm/s.

8. Apr 11, 2012

### Ereny

ohh kk .. why did they give me the velocity then.. doesnt that mean i have to use it?

9. Apr 11, 2012

### Staff: Mentor

Nope. Not to answer the question they gave you.

10. Apr 11, 2012

### Ereny

Last edited by a moderator: Apr 11, 2012