A ball is thrown upwards from the ground. It is at a height 100 m in upward and downward journeys at time `t_1` and ` t_2` respectively. If g = 10 `m/s^(2)`, then the product of `t_1 . t_2` is:

Options

A. 10
B. 20
C. 40
D. 50

Answer

b

Explanation

Here 100 =`ut-(1)/(2)g t^2=ut-5t^2`
or `5t^2 -ut+100=0`
There are two roots for this equation .Let `t_1` and `t_2` be the value. The product of the roots
`t_1.t_2=(100)/(5)=20`