Question

A man of mass 70 kg stands on a weighing scale in a lift which is moving:

(a) upwards with a uniform speed of 10 ms^-1.

(b) downwards with a uniform acceleration of 5 ms^-2.

(c) upwards with a uniform acceleration of 5 ms^-2. What would be the reading on the scale in each case?

(d) What would be the reading if the lift mechanism failed and it hurtled down freely under gravity?

Answer 1

The weighing scale will show reactions in each case:

(a) R = mg = 70 x 9.8 x 686 N

(b) R' = m(g - a) = 70(9.8 - 5) = 70 x 4.8 = 336 N

(c) R" = m(g + a) = 70(9.8 + 5) = 70 x 14.8 = 1036 N

(d) R'" = m(g - g) = 0