# Forced question

1. Aug 3, 2010

### quah13579

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

A barefoot water skier is towed behind a speedboat at constant velocity.
(i)
(a) Draw a side on diagram of the water skier and on your diagram label the directions and names of the forces acting on the water skier.

(b) What are two relationships between the magnitude of these forces?

(ii)
(a) When a ball is tossed straight up, it momentarily comes to rest at the top of its path. Is it in equilibrium during this brief moment? Give a reason for your answer.

(b) Consider a ball at rest in the middle of a toy wagon. When the wagon is pulled forward, the ball rolls backwards. Briefly account for this using Newton's first law.

3. The attempt at a solution
I am not sure how to do(i) .
(ii)(a) I think the answer is yes, but I am sure the reason.
(ii)(b) I understand the question, but I dont know how to use theory to explain this.

2. Aug 3, 2010

### Vaal

For (i) you will have three basic forces acting on the skier: gravity, the pull from the rope they are holding and the force of the water on there feet. (b) is getting at the fact that the skier is at a constant velocity therefore the forces must be in equilibrium according to newton's first law. Once you draw the force diagram it will be more apparent how this works.

In (i) (a) I believe the question is referring to equilibrium of forces. drawing a force diagram of the ball while it is in the air might help to answer this question.

In (i) (b) the question is worded a little funny. Another way to say the second sentence might be to say "When the wagon is pulled forward, the ball remains stationary (which is backwards relative to the wagon)". Again draw a force diagram and think about the forces acting on the wagon and the forces act on the ball, which is touching but not physically connected to the wagon.