# Quick work question.

1. Aug 1, 2007

### TexasCow

I'm working on some work problems.

Let's say we're moving an item up a 20* incline. It's mass is 150kg. The friction coefficient is .20.

Can gravity and/or normal forces "do" work?

Also, how does one calculate the minimum amount of force required to move this object at a constant speed?

Last edited: Aug 1, 2007
2. Aug 1, 2007

### gabee

Normal forces act in a direction perpendicular to the contact point on the plane. If you're talking about moving an object along a plane, the normal force can do no work since it's perpendicular to the object's direction of motion.

In this situation, however, gravity CAN do work. If you are moving the object up, against the force of gravity, gravity is doing negative work on the object.

Constant speed means no acceleration. By Newton's second law, if a = 0 then F = 0 also. Thus, to find the conditions for constant speed, you find the situation in which the total net force on the object is 0 (all forces cancel one another).

3. Aug 1, 2007

### TexasCow

Well for gravity, I did:

Wgravity=mgh=(150kg)(9.8)(sin30)

Is that correct?

4. Aug 1, 2007

### gabee

Only if you move it along the plane a distance of 1 meter. You know from trig that your height would be d*sinθ where d is the distance along the plane and θ is the angle of inclination of the plane. Other than that, it's right!