Phy 121
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For each situation state which of the five quantities v0, vf, `ds, `dt and a are given, and give the value of each.
• A ball accelerates uniformly from 10 cm/s to 20 cm/s while traveling 45 cm.
Since the problem is asking for the quantities that are given, the initial velocity (v0) in the above statement is 10 cm/s while the final velocity (vf) is 20 cm/s.
These quantities are correct. However there is another quantity given in the problem that you haven't mentioned.
• A ball accelerates uniformly at 10 cm/s^2 for 3 seconds, and at the end of this interval is moving at 50 cm/s.
In this statement, the quantities are the (a) acceleration which is 10 cm/s^2 and the final velocity (vf) is 50 cm/s.
There is also a third quantity given in this problem.
• A ball travels 30 cm along an incline, starting from rest, while accelerating at 20 cm/s^2.
In this statement, the initial velocity(v0) where it starts is 30 cm. The second quantity given is the acceleration (a) which is 20 cm/s^2.
There is at least one more quantity given in this problem.
Then for each situation answer the following:
• Is it possible from this information to directly determine vAve?
No, I think that the average velocity cannot be found because there needs to be at least 4 quantities available for a missing value to be found.
It is often possible to include a quantity from only to given quantities. However in each of the above, at least three quantities are given. Given three of these five quantities it is possible to find all the rest. However it is not always possible to find all the rest by reasoning directly from the given quantities, and it is not always possible to find the average velocity by reasoning directly from the given quantities.
The question here is whether it is possible to directly determine the average velocity in each of the three given situations. It is possible in at least one of these situations, and there is at least one situation in which it is not possible. You need to determine this possibility for each situation.
• Is it possible to directly determine `dv?
If we have final velocity, we can usually find the change in velocity.
This also requires a determination for each of the three given situations.
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I spent about 30 minutes to do this exercise.
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The quantities you identified were correct, but you didn't identify all the quantities given in each situation, and you didn't answer the questions about direct reasoning for each situation.
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