Question

A body dropped from top of a tower falls through ` 40 m` during the last two seconds of its fall. The height of tower in m is ( g= 10 m//s^@)`
A. (a) `10 m`
B. (b) ` 45 m`
C. (c ) ` 80`
D. (d)` 50 m`

Answer 1

Correct Answer - A
` S= 1/2 xx 10 xx t^2 ` and (S- 400 ) = 1/2 xx 10 (t-2)^2`
:. S- ( S- 40 0 = 5 T^2 - 5 (t- 2)^2`
or ` 40 = 20 t - 20 `or ` t= 3 s`
:. ` S = 1/2 xx 10 xx 3^2 = 45 m`.