Question

A ball thrown in the air reaches a height of 10 m and drops down to the ground. Find the time taken by the ball to complete this entire journey.

• A. 2.78 sec
• B. 3.40 sec
• C. 1.43 sec
• D. 2.86 sec

Answer 1

The correct option is D 2.86 sec

Given : Distance (s) = 10m
Final velocity = 0 m/s
Acceleration of gravity becomes acceleration of the ball, but since the ball goes upward the acceleration becomes - 9.8 m/s${}^2$.
By using the formula
$V^2=u^2+2as.$
$O^2=u^2+2\times -9.8\times 10$
$u^2=196$
$u=\sqrt{196}$
$u=14m/s$
Now we can calculate time by using
$V=u+at$
$O=14-9.8\times t$
$t=1.43s$
The time taken by the object to reach its highest point is equal to the time taken to come down. therefore the time taken by the ball to go upwards and return back will be
$1.43+1.43=2.86sec.$