IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

Apparent Weight

Objective

To study the apparent weight in accelerating situation.

Introduction

When a person stands on a weighing machine, the machine exerts an upward force $$N$$ on the person. This force $$N$$ is displayed on the scale in units of kg (1 kg-wt = 9.8 N). If the man accelerates or deaccelerates then $$N\neq mg$$ hence apparent weight (as measured by weighing machine) increases or decreases.

Apparatus

weighing machine used by doctors

Procedure

Stand on the platform of a weighing machine. Look at the reading of weighing machine. Now, bend your knees to lower yourself and see what happens to the reading. The reading will first decrease, may increase and decrease later, and finally become the same as normal reading.

Discussion

As you bend down, your centre of mass first accelerates in downward direction and then deaccelerates. Thus $$N>mg$$ in the beginning and \(N