# Homework Help: Force Problem all my answers don't work

1. Nov 13, 2012

### liamtcarroll

Assume you are on a planet similar to Earth
where the acceleration of gravity is approximately 10 m/s
and the positive directions for
displacement, velocity, and acceleration are
upward.
At time t = 0 s, an elevator is at a displacement of x = 0 m with a velocity of v = 0 m/s.
A student whose normal weight is 400 N
stands on a scale in an elevator and records
the scale reading as a function of time.

0-5sec------400
5-10sec-----700
10-15sec----0
15-20sec----200

what is the velocity of the elevator at the end of 20 sec

Last edited: Nov 13, 2012
2. Nov 13, 2012

### aralbrec

What does the scale measure?

Maybe a hint: if the elevator and person are not moving, the force the scale applies to the person standing on it must equal what?

3. Nov 14, 2012

### Basic_Physics

You need to determine the acceleration of the student during each period. Then draw a acceleration vs time graph and integrate it up to 20 s.

4. Nov 14, 2012

### Staff: Mentor

Stop posting questions showing zero effort. You *must* show your attempt at a solution in your schoolwork posts. Check your PMs.