How Does Student B's Acceleration Affect Student A's Position?

[metalmagik]

http://img213.imageshack.us/img213/6969/physicsproblemhq3.png

A rope of negligible mass passes over a pulley of negligible mass attached to the ceiling as shown above. One end of the rope is held by Student A of mass 70 kg, who is at rest on the floor. The opposite end of the rope is held by Student B of mass 60 kg, who is suspended at rest above the floor.

The first 2 questions asked for simple calculations, but now questions (d) and (e) ask:

(d) As Student B is accelerating at .25 m/s^2, is Student A pulled upward off the floor? Justify your answer.

Now I do not quite understand this..I guess it makes sense since the acceleration is so small, it doesn't have enough Fnet to make Student A go upwards. But (e) is as follows:

With what minimum acceleration must Student B climb up the rope to lift Student A upward off the floor?

I do not understand how to calculate this. I have the answer as 1.6 m/s^2 as per my teacher's key. If anyone could explain how to arrive at this answer please help me out! I have completed FBDs for these two Students so it would be fine to speak to me in terms of the forces. Thanks to anyone who could help me with this!

 

[Doc Al]

Hint: What tension is produced in the rope when Student B climbs? How much tension is needed to lift Student A?

 

[metalmagik]

AH i just got it. thanks for the response, I realized ForceNET. So I took the difference of Student A's weight and the tension on Student B and got acceleration from that. Thanks.