A rock is thrown up into the air with a speed of 15 m/s. How long does it take it to reach its highest point?

Question

What formula woud I use?

Answer 1

The initial velocity of the rock is (u) 15 m/s .

The final velocity of the rock when it reaches to maximum height is (v) = 0 .

Use the law of motion's first equation v = u + at .

Where v is the final velocity = 0 m/s .

          u is the initial velocity = 15 m/s .

          a is acceleration

          t is the time .

In this case the rock is thrown up so a = -g .

Acceleration due to gravity g = 9.8 m/s² .

v = u + at ⇒ v = u - gt

0 = 15 - 9.8(t)

9.8 t = 15

t = 15/9.8

t = 1.53 sec .

So the rock will reach the maximum height after 1.53 sec .