Question

Viru is standing on the top of the building of height 120 m and throws a ball vertically upwards with a speed of 10 m/s. Find the time taken by the ball to reach the ground. Take g = $10m{s}^{-2}$.

• A. 2 seconds
• B. 6 seconds
• C. 5 seconds
• D. 4 seconds

Answer 1

Answer: (B)

.Given,

Initial speed (u) =10 m/s

Time taken to reach at the maximum height

At maximum height velocity = 0

Acceleration due to gravity = 10 m/$s^2$

We know,

$v=u+at$

Putting all the values

$0=10-10\times t$

Or, t = 1 s

Maximum height

$s=ut+\frac{1}{2}a{t}^2$

$s=10\times 1-\frac{1}{2}\times 10\times 1^2$

Or, s = 5 m

Now time is taken to reach the ground from the maximum height

Total distance = 120 + 5 = 125 m

We know,

$s=ut+\frac{1}{2}a{t}^2$

Putting all the values

$125=0+\frac{1}{2}\times 10\times t^2$

After solving

t = 5 sec.

Hence the total time taken to reach the ground = 5 + 1 = 6 second

.