Question

A ball projected vertically upwards with speed u
from ground, rises to maximum height and then
returns back to same point. Find the average speed
of the ball.

Answer 1

Answer:

2u

Explanation:

At the highest point, velocity = 0.

Initial velocity = u

Final velocity = 0

Here, acceleration = - g(going upward) and g(coming downward)

Using the equations of motion:

• v = u + at

= > 0 = u + (-g)t

= > u/g = t

Total time taken to go and return = 2 * time taken to go

= > total time = 2*t = 2(u/g) = 2u/g

• v² = u² + 2aS

= > 0² = u² + 2(-g)S

= > u²/2g = S

Total distance to go and return = 2 * distance from ground to highest point

= > total distance = 2*S = 2(u²/2g) = u²/g

Therefore,

= > Average speed:

= > distance/time

= > (u²/g) / (u/2g)

= > (u² * 2g)/(g * u)

= > 2u