Space question (1 Viewer)

[jenslekman]

a load mass M rests on the floor of a lift which is accelearting upwards. the magnitude of the lifts acceleartion is a and the magnitrde of the acceleartion due to gravity is g. What is the magnitude of the resultant force acting on the load when the lift is finally at rest?

okay this is a past hsc question.

the answer is "mg" - but shouldnt it be zero because its asking for the RESULTANT force rather than the upwards force?

 

[Fizzy_Cyst]

is that the exact question?

If the lift is at rest and the mass is still on the floor of the lift, the weight force will be balanced by the normal reaction force and hence the resultant force would be zero?

Which paper is it from?

 

[clementc]

Woah dodgy question LOL. I think in this case it just means the instant at which the lift stops (having decelerated), the box is still slightly moving upwards, so the only force on it is gravity at that point.

 

[Fizzy_Cyst]

I found the question from a past HSC paper (really OLD one!), The answers said zero?

 

[D94]

(Assuming the question is correct) I don't know if I've missed something but the upwards acceleration is "a" (the lift) and the downwards acceleration is "g" (gravity). So we have a = g. Apply that to a load, so we get ma = mg, and since F = ma, the resultant force is mg.

Yes/no?

 

[Infinity Edu]

When the lift is moving, the resultant force is ma as the load is moving up at acceleration a.
When the lift is stationary, the resultant force is 0 as the load is not accelerating.