Need help on this problem

  • Thread starter unidentified4789
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  • #1
unidentified4789

Main Question or Discussion Point

A plane is traveling at 100m/s when it drops a box at an elevation of 2000 meters. How much time is required for the box to reach the earth?
 

Answers and Replies

  • #2
russ_watters
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You know the equation for freefall? Apply it to find the time and multiply the time by the speed of the plane.
 
  • #3
HallsofIvy
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What assumptions are you making? Are you ignoring air resistance? (If not, then you will have to state what the air resistance is.)

Assuming no air resistance, 2000 m is low enough that we can ignore the change in gravitational force due to change in distance so: the acceleration is 9.8 m/s2. The downward speed after time t is 9.8 t m/s and the distance fallen is 4.9 t2. The box will hit the earth when 4.9 t2= 2000.

The information about the horizontal speed of the airplane (and therefore the horizontal speed of the box) is irrelevant. The time to hit depends only on vertical acceleration and speed.
 
  • #4
russ_watters
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As someone informed me in a pm, I misread the problem. Sorry. Halls had it right. I was thinking of how far the box would move forward.
 

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