A 50-kg student (mg = 490 N) gets in a 1000-kg elevator at rest and stands on a metric bathroom scale. Sadly, the elevator cable breaks. What is the reading on the scale during the few seconds it takes the student to plunge to his doom?

It will be 0 newton

Explanation:

Basic concept to understand here is the increase and decrease in apparent weight of a body when elevator moves upward and downward. Remember, the mass does not change but apparent weight changes with the motion of elevator. It is due to the push by floor. Simply, if you standing on earth, the gravity pulls you down, but ground push you up, so both forces balance each other and you stand straight.

Notice that when elevator moves upwards, the apparent weight of a person increases which is due to the inertia and push of floor, our body resists to move upward so floor push us harder and we feel more weight.

Similar is the case for downward motion, when lift moves downward, our body which is at rest but its weight is acting downward. So, floor push us less harder against our original weight. So our apparent weight reduces.

Now in case of cable break, Lift will start to go along acceleration, there will be no floor and we would be like on the space, so their would be no apparent weight and weighing scale would show our weight 0