Physcis problem involving elevators?

Question

If a 91.2 kg person stood on the floor in an elevator accelerating upward with 0.78g, what would be the magnitude of the force exerted on the floor by the person? (b) What would be the magnitude of the force if the elevator were accelerating downward with 0.92g?


I've tried using the formula Fnet=W(mg)+N(ma) but I'm not getting the right answer. Can anyone help me out?

Answer 1

Your teacher can help

Answer 2

Ok. First and foremost, you're mixing metaphors. Weight is NOT the same thing as mass. So a kilo in mass terms is NOT the same as a kilo in weight.

Damn metric system can confuse people so much!

Here's where you're off:

F (Force) = mass * acceleration of gravity, that's the equation you're looking for.

W (WEIGHT) = mass * ACCELERATION component of the downward force.

Does that make sense?

So first and foremost, if you're dealing with the 'weight' component of kilos, then you want to convert that to mass using the system DEPENDENT conversion - this is where w=mg comes in, it converts from system dependent measures to system independent measures.

SO take this (w=mg)
91.2kg (weight) = m * 9.8 m/s, this gives you m=91.2/9.8= 9.306

THEN you take this equation for FORCE
F=ma

Your UPWARDS Acceleration is what 0.78g?

so f = 0.78 * 9.306, which equals 7.25868

You sound like you're not from the States. In the States, we are educated to understand this equation a bit better because we differentiate our mass measure from our weight measure. Mass is grams, and weight is pounds.

The 'metric' system' mixes metaphors, it confuses things a bit, by not recognizing weight and leveraging only mass. It can get confusing, right?

Good luck!