An elevator is moving down with uniform acceleration. A man inside the elevator who wants to measure the acceleration drops a coin as soon as the elevator starts. The coin is 6ft above the floor of the elevator at the moment it is dropped. It takes 1 second for the coin to reach the floor of the elevator. Calculate the acceleration from all this data.
How do I go about solving it ? I have absolutely no idea. Can anyone give at least some hints ?
Best Answer
Another possible way to solve it, is by using the elevator as the frame of reference. Since the elevator is accelerating downwards, we will have to apply a psuedo force upwards in the chosen frame of reference.Let a be the acceleration of the lift. Now the forces on the coin is mg(downward) and ma(upward).
Since the coin moves down when you drop it, by Newton's second law of motion, the net force is downward and hence net acceleration is also downwards and equal to $$g-a$$ According to the question, the ball hits the floor of the elevator in 1s travelling a distance of 6 feet=1.8288m.Apply $$s=ut+\frac {1}{2}a_{net}t^2$$ Here the ball is released from rest,so u=0,t=1s and s=1.8228m and $a_{net}$ is the net acceleration. Subustitue the values in the above equation and solve for a.