Phy 121
Your 'cq_1_8.1' 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 ball is tossed upward with an initial velocity of 25 meters / second. Assume that the acceleration of gravity is 10 m/s^2 downward.
• What will be the velocity of the ball after one second?
To find out the velocity here, we would need to find the velocity for an object thrown upward. v = v0 + at so in this case the equation would read 25 m/s – 9.8 m/s^2 (1.00s). The velocity of this ball tossed upward is -15.2 m/s.
25 m/s – 9.8 m/s^2 (1.00s) = +15.2 m/s, not -15.2 m/s.
• What will be its velocity at the end of two seconds?
After two seconds, the velocity will be -5.4 m/s.
Good, but should be +5.4 m/s, not -5.4 m/s.
• During the first two seconds, what therefore is its average velocity?
The average velocity I am guessing is -20.1 m/s.
You have enough information to find the average velocity with certainty. You know the velocity at the beginning of the interval, and at the end, and you know that the acceleration is uniform. What therefore it is the average velocity? Your guess of -20.1 m/s isn't very close, even if you change the - to +.
• How far does it therefore rise in the first two seconds?
• What will be its velocity at the end of a additional second, and at the end of one more additional second?
After 3 seconds, the velocity would be -4.4m/s and after 4 seconds, the velocity would be 14. 2 m/s.
• At what instant does the ball reach its maximum height, and how high has it risen by that instant?
I think that after the 4 seconds it has reached its maximum height and it has risen 39.2 meters.
• What is its average velocity for the first four seconds, and how high is it at the end of the fourth second?
The average velocity is 10.3 m/s and it is at least 40 meters high.
• How high will it be at the end of the sixth second?
I am guessing that after 6 seconds it would be at least 53 meters high.
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It took me 35-40 minutes to do this exercise.
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I got lost in this exercise because the wording was a bit hard for me to understand.
You have made a good attempt on the velocities, though you ended up with the wrong sign. You didn't get the correct average velocity, and didn't attempt to answer a couple of the questions. You might consider reworking these questions and using 10 m/s^2 as the acceleration of gravity rather than 9.8 m/s^2--the numbers will be much easier to keep track of, and less likely to distract you from the main purpose of this exercise. In any case most of your answers need at least a slight revision.
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