Question

A ball is dropped from a tower.in the last second of its motion it travel a distance of 15m.find the hight of tower

Answer 1

Given data states that in last second, ball travelled 15 meter and is being dropped so initial velocity is zero. Distance s travelled in last second = 15 m. therefore the time taken to travel the tower height before the last second be height $h-15=t-1$. From second equation of motion, we get $h=\frac { 1 }{ 2 } g{ t }^{ 2 }\Rightarrow h=5{ t }^{ 2 }$. Putting the values we get - $\Rightarrow h-15=\frac { 1 }{ 2 } g(t-1)^{ 2 }\Rightarrow 5{ t }^{ 2 }-15=5(t-1)^{ 2 }\Rightarrow t=2seconds$. Put the value of t in $h = 5t^2$, we get h = 20 m.