Homework Help: Reviewing for my exam (Newton question)

1. Nov 14, 2009

Chandasouk

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

You push a 20 kg box from an elevation of zero up a hill. You exert a force of 200 N for 6 m and the box speeds up steadily from rest to 2 m/s. There is a 100 N frictional force that opposes the box’s motion.

A) Draw energy bar charts to describe this motion. Be sure to describe your system, and the initial and final states.

B) At what elevation is the box moving when its speed is 2 m/s?

C) What angle does the hill make with the horizontal?

A) Initial (Bottom) Work = Final (Top) PE + KE+ $$\Delta$$Uinternal

B) Givens

m=20kg
F-applied = 200N
F-friction = 100N
V = 2m/s
L(distance traveled) = 6m

H= ?

Fd = mgh + .5mv2 + $$\Delta$$Uinternal

(200N)(6m) = (20kg)(9.80m/s^2)h + .5(20kg)(2m/s)^2 + (100N)(6m)

1200J = 196h + 40J + 600J

600J = 196h + 40J

560J = 196h

H = 2.86m

C) tan$$\theta$$ = 2.86/6 = 25.5 degrees

Not sure if anything is correct to be honest.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Nov 14, 2009

diazona

Actually I think that's about right. Just make sure you're using the right trigonometric function for the last step.