Question

A person of mass 70kg weighs himself on a weighing machine first on the earth and then on planet, where acceleration due to gravity is 1/2 that on the earth . Calculate the reading of weight on the weighing machineView Full Answer

Answer 1

(a). As the lift is moving at a uniform speed, acceleration a=0

R=mg

=70×10

⇒700N

Reading on the weighing scale

=700/g

=700/10=70kg

(b) Mass of the man, m=70kg

Acceleration, a=5m/s

2

downward

Using Newtons second law of motion, we can write the equation of motion as:

R+mg=ma

R=m(g−a)

=70(10−5)

=70×5

=350N

Reading on the weighing scale

⇒350g=350/10=35kg

(c) Mass of the man, m=70kg

Acceleration, a=5m/s

2

upward

Using Newtons second law of motion, we can write the equation of motion as:

R−mg=ma

R=m(g+a)

=70(10+5)=70×15

=1050N

Reading on the weighing scale

⇒1050/g=1050/10=105kg

(d) When the lift moves freely under gravity, acceleration a=g

Using Newtons second law of motion, we can write the equation of motion as:

R+mg=ma

R=m(g−a)

=m(g−g)=0

Reading on the weighing scale =0/g=0kg

The man will be in a state of weightlessness.

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