Question

Two balls are dropped to the ground from different heights. One ball is dropped $ 2\, s $ after the other but they both strike the ground at the same time. If the first ball takes $ 5\, s $ to reach the ground, then the difference in initial heights is $ (g=10m{{s}^{-2}}) $

• A. 20 m
• B. 80 m
• C. 170 m
• D. 40 m
• E. 160 m

Answer 1

Answer: (B)

$ {{s}_{1}}=\frac{1}{2}gt_{1}^{2}=\frac{10}{2}\times {{(5)}^{2}}=125\,m $
$ {{s}_{2}}=\frac{1}{2}gt_{2}^{2}=\frac{10}{2}\times {{(3)}^{2}}=45\,m $
$ \therefore $ $ {{s}_{1}}-{{s}_{2}}=125-45=80\,m $