A ball thrown vertically upwards returns to the ground in 13.5 seconds. With what velocity was it thrown up? (g = 10ms-2)

A ball thrown vertically upwards returns to the ground in 13.5 seconds. With what velocity was it thrown up? (g = 10ms-2) Correct Answer 67.5 m/s

The correct answer is 67.5 m/s.

Concept:

Kinematic equations of motion:

• These equations define the relationship between initial velocity u, final velocity v, time t, and displacement s of an object with respect to its motion in uniform acceleration a.
• Following are the three kinematic equations for uniformly accelerated motion:

⇒ v = u + at

⇒ s = ut + 0.5at2

⇒ v2 - u2 = 2as

Calculation:

Given

Time t = 13.5 s for going up and coming down

So for going up = t = 13.5/2 = 6.75

For going up initial velocity u = ?

At highest point velocity = v = 0

We know that,

v = u - gt

⇒ 0 = u - (10 × 6.75)

⇒ u = 67.5 m/s