Acceleration in an accelerated reference frame? Yes/no/maybe?

1. Apr 25, 2010

bigdog989

Hi, my question is this, say you’re in a lift that is accelerating downwards at 5ms and you were to drop a 200g wallet from say 1.3m off the floor of the lift, assuming gravity is 9.8ms, how long would it take the wallet to hit the floor of the lift?

Does the downwards acceleration of the life affect the time taken, im so unsure?

2. Apr 25, 2010

D H

Staff Emeritus
This looks like homework, bigdog989. Our policy on homework is pretty simple: We help you do your homework. We do not do it for you. You need to show some work on this topic before we can help you.

3. Apr 25, 2010

bigdog989

Oh fair enough, it's not really homework though, it's a question I found while reading up on referrence frams, but it gave no answer, as a student studying phyics it seemed quite interesting and I just want to find out how it all works, problem is I'm not entirely sure where to start, if they both started at rest this would be simeple but they don't

I'm sorry again I probably should have posted this in the homework section anyway

4. Apr 25, 2010

ideasrule

Think about it. If the lift accelerates downwards really quickly, do you feel lighter or heavier? The apparent force divided by mass is equal to acceleration. In this case, acceleration would be g-a: gravity provides g, but the elevator is accelerating at a, so the relative acceleration is g-a.

5. Apr 25, 2010

bigdog989

Oh ok, so I guess I’ve been over complicating this whole problem, you feel lighter as a lift accelerates downwards, thus you feel less acceleration..

So for this situation g-a = 9.8-5 = 4.8

Then I’d use
x=ut+1/2at^2
1.3=1/2 * 2.8 *t^2
1.3=1.4t^2
1.3/1.4=t^2
sqrt(1.3/1.4)=t

Would this be the way to work it out?