#$&*
Phy 201
Your 'cq_1_18.1' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
** **
A child in a slowly moving car tosses a ball upward. It rises to a point below the roof of the car and falls back down, at which point the child catches it. During this time the car neither speeds up nor slows down, and does not change direction.
What force(s) act on the ball between the instant of its release and the instant at which it is caught? You can ignore air resistance.
answer/question/discussion: ->->->->->->->->->->->-> :
Gravity will act on the ball at all times. Because the child or the roof of the car does not touch the ball then these do not have an force on it. The only other force I could think of would be the weight of the ball.
#$&*
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 rising the speed will decrease. When the ball is falling back down the speed increases. If we use a graph to analyze this we can see that as the ball rises the speed decreases at a constant rate with respect to time. When it falls the speed increases at a constant rate with respect to time. Therefore, the graph consists two straight-lines in a V shape.
#$&*
@&
The speed in the vertical direction is changing; the speed in the horizontal direction is not. The result will not be straight-line motion.
*@
Describe the path of the ball as it would be observed by someone standing along the side of the road.
answer/question/discussion: ->->->->->->->->->->->-> :
As observed from someone who is standing along the side of the road. The ball speeds up vertically, but does not horizontally. I believe that this will lead to a path that has a curvature to it.
#$&*
@&
Good.
*@
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: ->->->->->->->->->->->-> :
If the child is just coasting on the bike then the path of the ball will be about the same as before.
However, if the speed is greater. Air resistance will make the ball’s acceleration go backwards.
#$&*
@&
Unless the wind is blowing very hard, the ball will never go backwards.
However there will be an acceleration in the backward direction. Since the ball is moving forward, this will cause it to slow.
*@
What if the child drops the ball from the (inside) roof of the car to the floor? For the interval between roof and floor, how will the speed of the ball change? What will be the acceleration of the ball? (You know nothing about what happens after the ball makes contact with the floor, so there's no point in addressing anything that might happen after that point).
answer/question/discussion: ->->->->->->->->->->->-> :
The acceleration will increase until the ball hits the ground. The ball should have an acceleration of 9.8 m/s^2 because that is the force of gravity.
#$&*
@&
9.8 m/s^2 is the downward acceleration, which remains constant (as long as we can neglect air resistance due to the downward motion). The downward acceleration is not increasing or decreasing.
*@
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: ->->->->->->->->->->->-> :
If the air resistance is small, then the ball will continue to move horizontally alongside the car. The kid will see the ball drop straight down. The person observing this will see half of the curved path. They will see the ball move forward with the speed of the car.
#$&*
*#&!*#&!
&#Good responses. See my notes and let me know if you have questions. &#