# Need help on this problem

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?

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russ_watters
Mentor
You know the equation for freefall? Apply it to find the time and multiply the time by the speed of the plane.

HallsofIvy
Homework Helper
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.

russ_watters
Mentor
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.