A pine cone falls from a tall tree. It takes 0.2 seconds to pass by a 2 meter ta

Question

A pine cone falls from a tall tree. It takes 0.2 seconds to pass by a 2 meter tall window, i.e.the time between when it' s visible at the top of the window and when it has passed below the bottom of the window is 0.2 seconds.

How high above the window was it at its starting point?

Neglect air resistance

answer is either
5.1 meters
3.3 meters
2.6 meters
6.1 meters
4.15 meters

Suppose that the pine cone took 0.1 seconds to cross the window instead of 0.2 seconds.

What would that do to your answer for the starting height?

Explanation / Answer

Suppose its height above the window be h.

Velocity after dropping h distance is (2gh).

Using s = ut + 1/2*gt2 we get,

2 = (2gh)*0.2 + 1/2*9.81*0.22

This gives, h = 4.15 m

If the time taken were 0.1 second, we'll change 0.2 value with 0.1 in the above analysis.

So, 2 = (2gh)*0.1 + 1/2*9.81*0.12

This will give h = 19.4 m

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