How Do You Solve Physics Problems Involving a Pulley System with Two Students?

[driedupfish]

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.


(b) Calculate the magnitude of the force exerted by the floor on Student A.
(c) Student B now climbs up the rope at a constant acceleration of 0.25 m/s2 with respect to the floor.
Calculate the tension in the rope while Student B is accelerating.

(d) As Student B is accelerating, is Student A pulled upward off the floor? Justify your answer.

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

i was working on this question for a long time but i kept getting it wrong.

 

[Doc Al]

Show us what you've done so far and tell us where you are stuck. Here's a hint: Since the rope is masseless and the pulley is massless and frictionless, there will be a single tension throughout the rope.

 

[driedupfish]

i am now on part C, i think that since student A and B are both at rest at the first place, student B climbing up just adds another force to the tension, so .25 * mass of student B. = force of tension.

 

[Doc Al]

Careful. Newton's 2nd law tells you that the net force equals "ma". (Tension is not the only force on B.)

 

[physicshelpee]

How do you do this question?