Question:

A man will weigh more when

Updated On: Jul 5, 2022
  • lift accelerates upwards
  • lift accelerates downwards
  • lift descends freely
  • lift is going down
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The Correct Option is A

Solution and Explanation

When a lift accelerates upwards with uniform acceleration a $\therefore$ Apparent weight of man $R=m(g+a)$
When a lift accelerates downwards with uniform acceleration a $\therefore$ Apparent weight of man $R=m (g-a)$
When a lift descends freely $\therefore$ Apparent weight of man $R=m(g-g)=0$ [since $a=g]$ When a lift is going down (without acceleration), $\therefore$ Apparent weight of man $R=m(g-0)=mg$ [since $a=0]$ Hence, a man weigh more, when lift accelerates upwards
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Concepts Used:

Gravitational Potential Energy

The work which a body needs to do, against the force of gravity, in order to bring that body into a particular space is called Gravitational potential energy. The stored is the result of the gravitational attraction of the Earth for the object. The GPE of the massive ball of a demolition machine depends on two variables - the mass of the ball and the height to which it is raised. There is a direct relation between GPE and the mass of an object. More massive objects have greater GPE. Also, there is a direct relation between GPE and the height of an object. The higher that an object is elevated, the greater the GPE. The relationship is expressed in the following manner:

PEgrav = mass x g x height

PEgrav = m x g x h

Where,

m is the mass of the object,

h is the height of the object

g is the gravitational field strength (9.8 N/kg on Earth) - sometimes referred to as the acceleration of gravity.