A man of mass 70kg stands on a weighing scale in a lift which is moving:
A man of mass 70kg stands on a weighing scale in a lift which is moving:
A. upwards with a uniform speed of `ms^(-1)`
B. downwards with a uniform acceleration of `5ms^(-2)`
C. upwards with a uniform acceleration of `ms^(-2)`. What would be the readings on the scale in each case?
D. What would be the reading if the lift mechanism falled and it hurted down freely under gravity?
1 Answers
The reading on the scale is a measure of the force on the floor by the man. By the Third Law, this is equal and opposite to the normal force N on the man by the floor.
(a) `N=70xx10=700N`, Reading is 70kg
(b) `70xx10-N=70xx5`, Reading is 35kg
(c) `N-70xx10=70xx5`, Reading is 105kg
(d) `70xx10-N=70xx10`, Reading would be zero, the scale would read zero.