PHY 201
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A 70 gram ball rolls off the edge of a table and falls freely to the floor 122 cm below. While in free fall it moves 40 cm in the horizontal direction. At the instant it leaves the edge it is moving only in the horizontal direction. In the vertical direction, at this instant it is moving neither up nor down so, its vertical velocity is zero. For the interval of free fall:
• What are its final velocity in the vertical direction and its average velocity in the horizontal direction?
answer/question/discussion: ->->->->->->->->->->->-> :
We know the displacement in the vertical direction is 122 cm, and we are asked to find the final vertical velocity. We also know that the initial vertical velocity is 0 m/s. Then the final vertical velocity is: vf^2 = v0^2 + 2 a `ds = sqrt(0^2 m/s + 2 (-9.8 m/s^2) -1.22 m) = 4.89 m/s.
For the horizontal direction we know that the final velocity is 0 m/s, and it has a weight of .07 kg.
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• Assuming zero acceleration in the horizontal direction, what are the vertical and horizontal components of its velocity the instant before striking the floor?
answer/question/discussion: ->->->->->->->->->->->-> :
We know the horizontal component which is 40 cm, and the velocity it is going before it strikes the floor 4.89 m/s. Now we need to find the vertical component, which is the length just before the ground. I know that the ball falls a vertical length of 122 cm, but I am not sure how to get the vertical component of the velocity.
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• What are its speed and direction of motion at this instant?
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I think that the speed will be 4.89 m/s, but the direction I am not sure how to get???
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• What is its kinetic energy at this instant?
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The kinetic energy can be found by: .5 m v^2 = .5 (.07 kg) 4.89^2 m/s = .837 N.
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• What was its kinetic energy as it left the tabletop?
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For this I would have to have the horizontal final velocity, which I was unable to calculate.
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• What is the change in its gravitational potential energy from the tabletop to the floor?
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The gravitational PE at the floor is -.837 N, but I am not sure what the PE was when it left the table, which is the opposite and equal of the KE when it left the table. Then, you would subtract the two to get the
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• How are the initial KE, the final KE and the change in PE related?
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• How much of the final KE is in the horizontal direction and how much in the vertical?
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I do still not understand the vertical and horizontal projectiles. This seems blurry to me. How do you get the average velocity in the horizontal direction with the given information? Is what I answered so far correct? How would you get the direction at a instant of a fall, and the horizontal distance right before it striked the floor?
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45 Minutes
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