Question

A body falling freely under gravity passes two points 30 m apart in 1 s. From what point above the upper point it began to fall? (Take g = `9.8 m s^(-2)`).
A. 32.1 m
B. 16.0 m
C. 8.6 m
D. 4.0 m

Answer 1

Correct Answer - A
Suppose the body passes the upper point at t second and lower point at (t + 1) s, then
`S_2 - S_1 = 1/2 g(t - 1)^(2) - 1/2 "gt"^(2) = 1/2 g(2t + 1)`
or 30 m = `1/2 xx 9.8(2t + 1)` `therefore` t = 2.56 s
`S_1 = 1/2 "gt"^(2) = 1/2 xx 9.8 .. (2.56)^(2)` = 32.1 m.