posted by Mike

A ball is thrown upwards from a roof top, 80m above the ground. It will reach a maximum vertical height and then fall back to the ground. The height of the ball from the ground at time T is H, which is given by

H= -16t2 + 64t +80

1. Steve

well, you have the function. Using it, you can find the initial speed (64 ft/s), maximum height (at the vertex), and how long it takes to hit the ground (when h=0).

Incidentally, it is odd that the initial height is given in meters, but the -16t^2 is in ft/s^2.

2. Henry

I'm assuming that the ht. of bldg. is 80 FT.

V = Vo + g*Tr = 0.
64 + 32Tr = 0,
Tr = 2 s. = Rise time or time to reach max height, H.

H = -16*2^2 + 64*2 + 80 = 144 Ft.

0.5g*Tf^2 = 144.
16Tf^2 = 144,
Tf = 3 s. = fall time.

T = Tr + T = 2 + 3 = 5 s. = Time in flight.

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