Teaching Physics with the Physics Suite Edward F. Redish

Ball on a ramp

 The figure at the right shows a multiple-exposure photograph of a ball rolling up an inclined plane. (The ball is rolling in the dark, the camera lens is held open, and a brief flash occurs every 3/4 sec four times.) The left-most ball corresponds to an instant just after the ball was released. The right-most ball is at the highest point the ball reaches.

1. Copy this picture on your paper and, at each ball, draw an arrow to indicate the velocity of the ball at the instant when it was at that point in space. Explain what is happening ("tell the story" of the picture).

2. For the instant of time when the ball is at the second position shown from the left, draw a free-body diagram for the ball and indicate all forces acting on it.

3. If your force diagram doesn't include an arrow pointing up the ramp, explain why the ball keeps rolling up the ramp.

4. If the mass of the ball is m, what is its acceleration?

5. If the angle q is equal to 30o, how long is the distance s?

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