# Simple work question

1. Oct 15, 2006

### sundeepsingh

A book is pushed up a ramp by a force. Calculate the net work done by :

a. Fpush
b. Fgrav
c. Fnormal

Let fnet = 5 newtons and displacement of the object be 5 m up the ramp,
so the net work done by Fpush = 5 * 5 = 25 J. is the Work net by grav = mgsin@ * 5? and net work by Fnormal = mgcos@ * 0.5? is the work of gravity negative and Fnormal positive? Kindly guide me to the correct answers. Thanks

2. Oct 15, 2006

### gunblaze

Fpush is right. For part b and part c. You do need to understand that the work is done only by multiplying the force and the distance parallel to the direction of the force.

3. Oct 15, 2006

### Andrew Mason

Keep in mind that Work is a dot product of the force and displacement vectors. So:

$$W = Fd\cos\theta$$

So for c. what is the angle between the force and the displacement? What is the cos of that angle?

For b, what is the angle between the gravitational force and the displacement in terms of $\alpha$, the angle of the ramp above the horizontal? (your answer is right here, but the analysis is not clear).

You have it right for a.

AM

4. Oct 16, 2006