Answer:
Average speed, over the first 4.0 s of its motion, of a pebble released from rest off a bridge = 19.6 m/s
Explanation:
We have equation of motion , [tex]s= ut+\frac{1}{2} at^2[/tex], s is the displacement, u is the initial velocity, a is the acceleration and t is the time.
In this case the initial velocity of body = 0 m/s, acceleration = 9.8 [tex]m/s^2[/tex], we need to calculate displacement when t = 4 seconds.
Substituting
[tex]S=0*t+\frac{1}{2} *9.8*4^2\\ \\ S=78.4 meter[/tex]
So a distance of 78.4 meter has been traveled by pebble in 4 seconds.
Average speed = 78.4/4 = 19.6 m/s
