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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.
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cq_1_181
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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.
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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: ->->->->->->->->->->->-> : ->->->->->->->->->->->-> :
&&&&&Gravity
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Muscle force doesn't act until the ball makes contact with the hand. If you consider the ball caught only when it has come to rest, which is a valid interpretation, then there is a brief phase of motion in which the muscle force does act, but for most of the interval it does not.
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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: ->->->->->->->->->->->-> : ->->->->->->->->->->->-> :
Speed is the greatest going up and slowing down due to gravity. Reaches full height then falls and begins to speed up with help from gravity.
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Describe the path of the ball as it would be observed by someone standing along the side of the road.
answer/question/discussion: ->->->->->->->->->->->-> : ->->->->->->->->->->->-> :
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Ball will go up and then come back down and for the observer it will be moving forward with the car.
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Observed from the side of the road the ball will also be moving forward.
What therefore would be the shape of its path, observed from the side of the road?
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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: ->->->->->->->->->->->-> : ->->->->->->->->->->->-> :
Nothing different if on a bike, but will continue to the ground if not caught.
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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: ->->->->->->->->->->->-> : ->->->->->->->->->->->-> :
&&&Velocity is increases until ground. Acceleration is 9.8m/s^2&&&
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If acceleration is always 9.8 m/s^2, as will be the case if we ignore air resistance (which is pretty much ignorable at these speeds), then the acceleration is constant, not increasing.
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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 child throws the ball outside of the car the path of the ball does not change but from the outside and because the car is moving the ball toss is move towards the back of the car but ball is still in forward motion.&&&&&&
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If air resistance is negligible then there is no force to slow the ball's forward motion, so the forward motion will continue with no change in velocity.
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A child in a car tosses a ball upward so that after release it requires 1/2 second to rise and fall back into the child's hand at the same height from which it was released. The car is traveling at a constant speed of 10 meters / second in the horizontal direction.
Between release and catch, how far did the ball travel in the horizontal direction?
answer/question/discussion: ->->->->->->->->->->->-> : ->->->->->->->->->->->-> :
ds=vAVe*'dt=10m/s*.5s=5m
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As observed by a passenger in the car, what was the path of the ball from its release until the instant it was caught?
answer/question/discussion: ->->->->->->->->->->->-> : ->->->->->->->->->->->-> :
It would rise and slowly stop then pick up speed on the way back down.
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Sketch the path of the ball as observed by a line of people standing along the side of the road. Describe your sketch. What was shape of the path of the ball?
answer/question/discussion: ->->->->->->->->->->->-> : ->->->->->->->->->->->-> :
Parabolic.
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How fast was the ball moving in the vertical direction at the instant of release? At that instant, what is its velocity as observed by a line of people standing along the side of the road?
answer/question/discussion: ->->->->->->->->->->->-> : ->->->->->->->->->->->-> :
v0= 'ds-.5*a*'dt^2
v0=0-.5*9.8m/s^2*.5s^2
v0=2.45m/s
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How high did the ball rise above its point of release before it began to fall back down?
answer/question/discussion: ->->->->->->->->->->->-> : ->->->->->->->->->->->-> :
vAve=(2.45m/s+0)/2=1.23m/s
'dv=(0-2.45m/s)=-2.45m/s
'dt=-2.45m/s/9.8m/s^2=.25s
vAve*'dt='ds=1.23m/s*.25s=.31m
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&#Good responses. Let me know if you have questions. &#