posted by Robert C on .
A ball, dropped from rest, cover 2/7 of the distant to the ground in the last 2 seconds of its fall. From what height was the ball dropped? What was the total time of the fall?
Let T be the total time to hit the ground.
Let H be the height it is dropped from.
H = (g/2) T^2
(5/7) H = (g/2)(T-2)^2
Two equations, two unknowns. H can be eliminated easily.
(5/7)H = (5/14) g T^2
(5/7)H = (g/2)(T-2)^2
Solve for T first, then solve for H