Phy 121
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A child in a slowly moving car tosses a ball upward. It rises to a point below the roof of the car and falls back down, at which point the child catches it. During this time the car neither speeds up nor slows down, and does not change direction.
• What force(s) act on the ball between the instant of its release and the instant at which it is caught? You can ignore air resistance.
answer/question/discussion: ->->->->->->->->->->->-> :
The force that acts on the ball between the instant of release and the instant at which it is caught is gravity.
• What happens to the speed of the ball between release and catch? Describe in some detail; a graph of speed vs. clock time would also be appropriate.
answer/question/discussion: ->->->->->->->->->->->-> :
As the ball is thrown up it loses speed, and when it is falling back down it gains speed, because the force of gravity.
• Describe the path of the ball as it would be observed by someone standing along the side of the road.
answer/question/discussion: ->->->->->->->->->->->-> :
If someone was observing the path of the ball from along side of the road, the path would look like the ball was moving to the left.
• How would the path differ if the child was coasting along on a bicycle? What if the kid didn't bother to catch the ball? (You know nothing about what happens after the ball makes contact with the ground, so there's no point in addressing anything that might happen after that point).
answer/question/discussion: ->->->->->->->->->->->-> :
The speed of the ball would not be as fast as it was in the car. When the ball is thrown up in the car it is going the same speed as the car, and when thrown up while riding the bicycle, the ball is going the same speed as the bicycle. If the kid didn’t catch the ball then the ball would hit the kid and fall to the ground, assuming that the kid was throwing the ball in front of him. If he was throwing it from the side then the ball would go flying behind the bicycle and hit the ground.
• What if the child drops the ball from the (inside) roof of the car to the floor? For the interval between roof and floor, how will the speed of the ball change? What will be the acceleration of the ball? (You know nothing about what happens after the ball makes contact with the floor, so there's no point in addressing anything that might happen after that point).
answer/question/discussion: ->->->->->->->->->->->-> :
Assuming that the car is moving and the kid drops the ball from the roof to the floor, then the ball will move towards the kid. The acceleration and speed of the ball will increase, because gravity is pulling down on the ball.
• What if the child holds the ball out of an open window and drops it. If the ball is dense (e.g., a steel ball) and the car isn't moving very fast, air resistance will have little effect. Describe the motion of the ball as seen by the child. Describe the motion of the ball as seen by an observer by the side of the road. (You know nothing about what happens after the ball makes contact with the ground, so there's no point in addressing anything that might happen after that point).
answer/question/discussion: ->->->->->->->->->->->-> :
The motion of the ball seen by the child would be that the ball looks like it is falling in a straight line until it hits the ground. If an observer from the side of the ball saw the ball fall the motion of the ball would look like the ball was moving to the left until it hit the ground.
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30 minutes
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Your answers a good and very well expressed, but be sure to see the discussion at the link.
&#Please compare your solutions with the expanded discussion at the link
Solution
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