# Homework Help: Power physics question

1. Jan 5, 2008

### imy786

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

Determine the power required to pull a body of mass m up a smooth plane
inclined at an angle a to the horizontal at a constant speed Vo. Explain why
it is unnecessary to specify the direction in which the applied force is acting.

2. Relevant equations

Power= work done /time
work done= force * distance
Force= mg

3. The attempt at a solution

Power= mg/ time

2. Jan 5, 2008

### Staff: Mentor

mg is the force, not the work done.

3. Jan 5, 2008

### imy786

Power= work done /time
work done= force * distance
Force= mg

power= mgd

4. Jan 5, 2008

### nonequilibrium

now you forgot the time element

5. Jan 5, 2008

### Staff: Mentor

Do it step by step. If the angle is "a", what force is required to move the body at constant speed? Say you move the object a distance "d" up the incline, how much work is required? How much time is required, if the speed is v0? What's the power required?

6. Jan 5, 2008

### imy786

Power= work done /time
work done= force * distance
Force= mg

Power= force * distance / time
= mg * d /t
= veloctiy *mg

7. Jan 5, 2008

### Staff: Mentor

Your answer should be in terms of the angle and the speed.

8. Jan 5, 2008

### imy786

power= vsine mg

9. Jan 5, 2008

### Staff: Mentor

Right. $P = mg \sin (a) v_0$.

10. Jan 5, 2008

### imy786

doc...can you show me how to arrive to get sin in the solution..i know its by resolving..but can you pelase provide details thanks

11. Jan 5, 2008

### Staff: Mentor

Since the object moves at constant velocity, the net force on it must be zero. Since it moves along the incline, examine forces in that direction. Since the component of gravity parallel to the incline is $mg\sin\theta$ downward, the applied force must have an equal component parallel to the incline pointing upward. Make sense?

Note: Since the object moves parallel to the incline, only force components parallel to the incline contribute to work done.