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Mechanics 1 help needed- newtons 2nd law

Right I'm really stuck on this question, I think the wording is confusing me a fair amount :frown:

a lift descends with an acceleration of 1.5ms-2, then moves at a constant speed until it's retarded at 1ms-2. A package of mass 20kg stands on the floor of the lift during the journey. Find the magnitude of the force it exerts on the floor of the lift at each stage.

Okay- so i'm unsure as to how many stages there are- is it 2 or 3?
Wouldn't the magnitude of the force just be mass x g anyway so it'd just be 196N for all stages?
Somebody help me (or at least point me in the right direction!)

also I tried working out the resultant force on the package when the lift was descending and found it to be -10N, that can't be right can it?!

Reply 1

jaroc

Original post by mammamia:0

Right I'm really stuck on this question, I think the wording is confusing me a fair amount :frown:

There are three stages.
Think of acceleration of the package. In the first stage it's 1.5 m/s^2 downwards, in the second stage it's 0, in the third it's 1 m/s^2 directed upwards.
There are two forces that act on the package - gravitational force

mg

acting downwards and the normal force (equal in magnitude to the force the package exerts on the floor) acting upwards. The resultant force of those two forces makes the package accelerate.

Hope this is clear enough.