Some conceptual questions

  • Thread starter mikefitz
  • Start date
  • #1
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I was looking through my book tonight before my midterm exam and came across the following conceptual questions I would like to discuss before I take the test.

A rock is thrown straight up. It reaches the top of its path and starts to fall back down. It’s acceleration on the way down, neglecting air resistance, is:
(a) greater than when it was at the top of its path.
(b) the same as when it was at the top of its path.
(c) less than when it was at the top of its path.


Acceleration on the way down due to gravity would be 9.8m/s^2. However, couldn't the acceleration on the way up be greater than that? (IE: If I were to fire a bullet straight up it would have an acceleration greater than 9.8)

A ball is launched from ground level with initial velocity components vox and voy and flies through the air, reaching a maximum height, having a certain time of flight, and reaching a certain range. How will EACH of these 3 quantities change (increase/decrease/unchaged) if we increase vox (but keep voy at its original value)?

Maximum Height-- Time of Flight-- Range
(a) increase increase increase
(b) unchanged unchanged increase
(c) decrease decrease decrease
(d) increase unchanged unchanged
(e) decrease increase unchanged


Changing Vx wouldn only change the range since x/y components are independent, correct?



A passenger who weighs 180 lbs stands on a scale in an elevator. The scales read 190 lbs. The elevator could be
(a) moving upward and increasing its speed
(b) moving upward and decreasing its speed
(c) moving downward and increasing its speed
(d) moving downward at a constant speed


Probably moving upward and increasing in speed since there is a net force on the person greater than their weight.


Thoughts?
 

Answers and Replies

  • #2
rsk
283
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mikefitz said:
However, couldn't the acceleration on the way up be greater than that? (IE: If I were to fire a bullet straight up it would have an acceleration greater than 9.8)
Why - what forces are acting on it at this point?

Probably moving upward and increasing in speed since there is a net force on the person greater than their weight.
Thoughts?

If there is an apparent increase in mass, this means that they are acceerating upwards, or decelerating downwards. So really, there are two possibilities although your choice of 4 answers only includes 1 of them.
 

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