Question

A lift is moving with constant acceleration upwards,the mass of the object in the lift will increase or decrease
.

Answer 1

As you know mass is material property , it can't be change in any situation.
But weight may be change and effected by gravity, Because weight is the product of mass and acceleration due to gravity.

Now, question said " A lift is moving upward direction with constant acceleration.it means lift is moving in non- inertial frame . But we know Newton's law can't valid in non- inertial frame so, we have to use the concept of Psuedo force for making inertial frame of reference.
Let a is the acceleration of lift in upward direction.
so, we have to apply Psuedo acceleration a just opposite direction of it.
e.g., Pseudo force = ma acts downward in object.
Now, net downward force act on object = mg + ma = m(g + a) > mg

It means object will be heavier. I mean weight of object will be high , But mass will be constant

Answer 2

At the beginning,

When the elevator is accelerating downward,

• It reaches a steady speed.
• Your weight becomes  normal

Then it decelerates downward as it comes to a stop at the ground floor.  

Inference:

• Weigh is less at the beginning when the elevator moves down
• Weight is more at the end when the elevator moves down

Hence, his weight is less at the beginning of the trip down and more when the lift reached the ground floor.

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