Question

A ball is thrown vertically upwards from the ground. It crosses a point at the height of $25m$ twice at an interval of $4secs$. The ball was thrown with the velocity of

• A. $20m/sec$.
• B. $25m/sec$.
• C. $30m/sec$.
• D. $35m/sec$.

Answer 1

The correct option is C $30m/sec$.

At the point 25m above it takes 4 sec. i.e., time of flight there is 4 s.
$4=\frac{2u}{g}u=20m/s$
at 25m height it has velocity 20m/s and it goes further height of $\frac{u^2}{2g}=20m$
Total max height $=20+25=45m$
Initial velocity.
$45=\frac{u^2}{2g}u=30m/s$