I'm new to this stuff, so the question may be really simple, but I just can't work it right... Alright, so the question I'm trying to figure is this: The student's normal weight is 500 N. He stands on a scale in an elevator and records the scale reading as a function of time. So for the first 5 seconds the scale is at 500 N, thus the acceleration is 0 m/s/s. Then the next 5 seconds the scale reading is at 700. Now how do I go about figuring the acceleration? I know F=ma. The only way I could think of solving this problem is putting the difference in for the force variable, the students weight in for the mass variable and then solving for acceleration. So for example for the second 5 seconds I used 200=500a and I got 0.4 m/s/s. This doesn't seem like the right answer so I must be missing something or just going about the problem completely the wrong way. If someone could point me in the right direction I'd really appreciate it!