PHYSICS...please help me?

Question

An inventive child named Chris wants to reach an apple in a tree without climbing the tree. Sitting in a chair connected to a rope that passes over a frictionless pulley, Chris pulls on the loose end of the rope with such a force that the spring scale reads 327.5 N. Chris's true weight is 465 N, and the chair weighs 173 N. The acceleration of gravity is g=9.8 m/s^2. Find the magnitude of the acceleration of the system. Answer in units of m/s^2.

Had to miss like 5 of my physics classes, have no idea whats going on or how to do any of the problems on my worksheet, any help would be greatly appreciated. Thanks.

Answer 1

I assume the spring scale is weighing the chair and Chris, yes?

Look at a FBD of the chair

The tension in the rope is
327.5 N since it is continuous around the frictionless pulley.

The net weight of Chris and the chair is reduced by 327.5 since he is applying that force to the downward rope,

so the downward force is
465+173-327.5
or
310.5 N

That means the net upward force on Chris and the chair is
17 N
and, using F=m*a
calculate m
m=(465+173)/9.8
=65.1 kg

therefore

17=65.1*a
and
a=0.261 m/s^2

j