1 kg wt = 9.8N, so 2.5 kg wt = the gravitational force on a 2.5 kilogram weight, 24.5N
We can do this question in kg wt or N, both are a unit of force. we'll use N for simplicity
Okay also what are we looking for? normal force at rest and normal force at a=+2
so let's look for the mass because that will let us find the two things above
so when the lift has a=-1 the apparent weight (i.e. the normal force) of the body is 2.5kgwt=24.5N
what are the forces acting here? well we have W=mg and Normal force, and we know that normal force is 24.5N.
Normal is pointing up, weight is pointing down and ofc net is down because we're accelerating downwards.
Fnet = ma
Weight + Normal = ma
m*-9.8 + 24.5 = m*-1
m(8.
=24.5
m=2.78kg
woo so now we have the mass, everything will start fall into place
"what's the reading if the lift is at rest?"
well at rest, a=0 so;
Fnet = ma
W-N=0
N=W
N = mg = 27.3N
but we probably want it in kg wt because that's how the question was asked,
so we could divide by 9.8 OR realise that the reading will just be the mass of the object
since that's how the kg wt is defined
reading = 2.78kg wt
"accelerating up at 2m/s^2"
W + N = ma
N = m*2 - m*-9.8
N = 2.78*11.8
N = 32.85Newtons
N = 3.35kg wt
when accelerating downwards, the apparent weight was less than actual weight because we were falling so the normal force (apparent weight) didn't have to hold the body up
at rest, they're equal because the normal force has to oppose weight force exactly (or you'd be falling)
and when accelerating upwards, the force required is more than at rest because you have to push up against gravity and have a net upwards force
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