Question

Suppose a rock is dropped off a cliff with an initial speed of 0m/s. What is the rocks speed after 5 secounds, in m/s, if it encounters no air resistance?

Answer 1

Answer:

50 m/s

Explanation:

u = 0 m/s, t = 5 seconds, v = ? , g = 10 m/s^2

Use first equation of motion

v = u + g t

v = 0 + 10 x 5 = 50 m/s

Answer 2

Answer:

The rock's speed after 5 seconds is 98 m/s.

Explanation:

A rock is dropped off a cliff.

It had an initial velocity of 0 m/s. And now it is moving downwards under the influence of gravitational force with the gravitational acceleration of 9.8 m/s².

Speed after 5 seconds = V

We know that acceleration = average speed/time

In our case,

g = ((0+V)/2)/5

9.8*5 = V/2

=> V = 2*9.8*5

V = 98 m/s