Question

A girl is 13m away from a tree. An apple falls from the tree at height of 2.8 m. If she wants to catch the apple before it hits the ground then how fast does she need to run?

• A. $9.83m{s}^{-1}$
• B. $0.755\frac{m}{s}$
• C. More information is needed to solve
• D. $17.22m{s}^{-1}$
• E. $1.33\frac{m}{s}$

Answer 1

The correct option is D $17.22m{s}^{-1}$

Height of the tree $h=2.8$ m

Distance of girl from tree $d=13$ m

Time taken by apple to reach the ground $t=\sqrt{\frac{2h}{g}}=\sqrt{\frac{2\times 2.8}{9.8}}=0.76$ s

Thus the speed of the girl $v=\frac{d}{t}=\frac{13}{0.76}=17.11\simeq 17.22$ m/s