An elevator is being pulled up from the ground floor to the third floor by a cable. The cable is exerting 4500 newtons of force
on the elevator. According to Newton's law of action-reaction, what is the gravitational force on the elevator, in newtons, if the elevator is NOT accelerating?
The acceleration of the elevator = Not accelerating
From Newton's third law of motion, the action of the cable force is equal to the reaction of the gravitational force on the elevator which is the weight, W and motion of the elevator as follows;
F = W + Mass of elevator × Acceleration of elevator
∴ F = W + Mass of elevator × 0 = W
F = 4500 N = W
The net force on the elevator is F - W = 0
The gravitational force on the elevator = W = 4500N.
Approximately (assuming that , the ball was launched from ground level, and that the drag on the ball is negligible.)
Explanation:
Let denote the velocity at which the ball was thrown upward.
If the drag (air friction) on the ball is negligible, the ball would land with a velocity of exactly . The velocity of the ball would be changed from to (such that ) within .
Also because the drag on the ball is negligible, the acceleration of the ball would be . Thus:
.
Since :
.
.
The ball reaches maximum height when its velocity is . Apply the SUVAT equation to find the displacement between the original position (ground level, where ) and the max-height position of the ball (where .)