BITSAT 2018 Paper

We have, a =

d2x

dt2

= - 9.8
The initial conditions are x (0) = 19.6 and v (0) = 0
So, v =

dx

dt

= - 9.8t + v(0) = - 9.8t
∴ x = -4.9 t2 + x (0) = - 4.9 t2 + 19.6
Now, the domain of the function is restricted since the ball hits the ground after a certain time. To find this time we set x = 0 and solve for t.
0 = - 4.9 t2 + 19.6
⇒ t = 2