Man pulling himself up at 0.2m/s^2

[thedarkone80]

Homework Statement

A man with an 70kg mass, sits on chair of 10kg, and pulls himself upwards at a acceleration of 0.2m/s^2. What is the force needed to achieve this acceleration?

Homework Equations

F=ma

The Attempt at a Solution

F=(80)*(9.81+0.2)
F=(80)*(9.81-0.2)
Neither are giving a correct answer, please help!

 

[Seannation]

Well, he's not going to take the chair with him when he pulls himself up, I take it? So the mass is 70kg only.

Remember that the force of gravity is acting in the opposite direction to the direction the man is accelerating in. Taking the direction of acceleration due to gravity to be positive, and the direction of acceleration of the man to be negative (since it is against gravity) then the overall acceleration is 9.81 + (-0.2) = 9.61.

 

[thedarkone80]

no, he is pulling himself and the chair upwards, he is on a pully system. sorry for not being clear. appreciate the quick response though!

 

[Redbelly98]

Homework Statement

A man with an 70kg mass, sits on chair of 10kg, and pulls himself upwards at a acceleration of 0.2m/s^2. What is the force needed to achieve this acceleration?

Homework Equations

F=ma

The Attempt at a Solution

F=(80)*(9.81+0.2)
F=(80)*(9.81-0.2)
Neither are giving a correct answer, please help!

One of these last 2 equations is correct (do you know which?) There might be a problem with the number of significant figures you gave in your answer, or you could have done the arithmetic wrong. Since you didn't say what answer you got, it's hard to tell.

 

[Redbelly98]

no, he is pulling himself and the chair upwards, he is on a pully system. sorry for not being clear. appreciate the quick response though!

Just read this more carefully, I didn't realize before there is a pulley system involved.

Have you drawn a free body diagram for the man+chair? In how many different places is a rope attached to them, including where the man is holding the rope to pull himself up?