Physics Relative Acceleration of Pulley?

Question

A man with mass 70.0 kg stands on a platform with mass 25.0 kg. He pulls on the free end of a rope that runs over a pulley on the ceiling and has its other end fastened to the platform. The mass of the rope and the mass of the pulley can be neglected, and the pulley is frictionless. The rope is vertical on either side of the pulley.

Question: What is the acceleration of the rope relative to him?

the platform has an upward acceleration of 1.8 m/s
And I have found the force he needs to pull is 551N

3.6 m/s^2 didn't come out as the right answer...

Answer 1

If the acceleration of the platform w/r/t the Earth is 1.8 m/s^2
then that means that y(t)=.5*1.8*t^2

since the rope has the same acceleration upward and downward, then w/r/t the man, a particle of the rope must have y(t)=0 on the platform side, and y(t)=-2*.5*1.8*t^2 on the other side, so the acceleration of the rope w/r/t the man is
3.6 m/s^2

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Answer 2

draw a loose physique diagram. you pick for to stability the forces. on the grounds that there is a incline, the classic stress is mgsintheta (assuming theta is the recommendations-set of the incline). the friction stress is then the classic stress circumstances the coefficient. in case you recognize the stress stress, it rather is a similar because of fact the friction stress, so as which you will freshen up for theta. i choose that works. I extremely have a physics examination thursday!!