Answer:
The person on the truck would have the same speed as that of the truck. Also, before the ball is thrown, the ball would have the speed as that of the truck.
It is possible for a person standing at the side of the road to view the falling straight down. This would be possible if the ball is thrown backwards with the same magnitude of velocity as that of truck.
To the person on the truck, the ball would appear to have forward motion with the speed of the truck.
The object is fixed relative to the motion you are trying to describe.
-- When the ball is at the top, before it's dropped, it has potential energy above the equilibrium position.
Potential energy = (mass) x (gravity) x (height) = (mass) x (G) x (0.5)
As it passes through the equilibrium position, it has kinetic energy.
Kinetic energy = (1/2) x (mass) x (speed)²
How much kinetic energy does it have at the bottom ?
EXACTLY the potential energy that it started out with at the top !
THAT's where the kinetic energy came from.
So the two expressions for energy are equal.
K.E. at the bottom = P.E. at the top.
(1/2) x (mass) x (speed)² = (mass) x (G) x (0.5)
Divide each side by (mass) . . .
(the mass of the ball goes away, and has no effect on the answer !)
(1/2) x (speed)² = (G) x (0.5)
Multiply each side by 2 :
(speed)² = G
speed = √G = √9.8 = <u>3.13 meters per second</u>, regardless of the mass of the ball !
