Скачать или смотреть Apparent Weight of a man in a Lift and Law of Conservation of Momentum

Apparent weight of a man in a lift:
Let a man of mass m is standing on a weighing machine placed in a lift or elevator. The actual weight mg of man acts on weighing machine and it offer a reaction R given by treading of weighing machine.
The reaction R exerted by the surface of contact on the man is apparent weight of the person. The value of R (apparent weight) comes out different in different situation.
i) When the lift moves upwards with acceleration a as shown in figure, the net upward force on the man is R – mg
Therefore R-mg = ma  R = ma + mg
Apparent weight = R = m (g + a)
So, when lift accelerate upwards, apparent weight of the man inside it increases.
ii) When the lift accelerates downwards with acceleration a as shown in figure:
The net downward force on the man is mg -R = ma
The apparent weight, R = m(g-a)
So, when lift accelerate downwards, apparent weight of the man inside it decreases.
iii) When the lift is at rest or moving with constant velocity v (a= 0) downward or upward as shown in figure.
Since, acceleration is zero a = 0, so the net force on the man is
R – mg = mx0
 R = mg
Apparent weight = Actual weight.
So, when lift is at rest or moving with constant velocity, the apparent weight of a man is equal to his actual weight.
Law of conservation of linear Momentum: The total momentum of an isolated system (No external force) remains constant or conserved.

i.e. Total momentum before collision = total momentum after collision.
Please see the complete video for better understanding


The videos will contain the content as per the CBSE board. The content will also help to those students who are going to appear in NEET or JEE Exams.