What Force Must a Window Washer Exert to Ascend at Constant Speed?

[meganw]

Homework Statement

A window washer pulls herself upward using the bucket-pulley apparatus:

The mass of the person plus the bucket is 63 kg.

(a) How hard must she pull downward to raise herself slowly at constant speed?

Homework Equations

F = m(a)

The Attempt at a Solution

I figured that since she wants to raise herself at constant speed, that makes her acceleration equal to zero. Which means Fnet=0=Ftension-Fgravity, so Ftension=Fgravity. F gravity=9.8(63)=617.4 N, but it says I have the wrong answer.

Thanks in advance for the help.

 

[PhanthomJay]

Homework Statement

A window washer pulls herself upward using the bucket-pulley apparatus:

The mass of the person plus the bucket is 63 kg.

(a) How hard must she pull downward to raise herself slowly at constant speed?

Homework Equations

F = m(a)

The Attempt at a Solution

I figured that since she wants to raise herself at constant speed, that makes her acceleration equal to zero. Which means Fnet=0=Ftension-Fgravity, so Ftension=Fgravity. F gravity=9.8(63)=617.4 N, but it says I have the wrong answer.

Thanks in advance for the help.

you need to draw a good free body diagram. Isolate the woman , bucket and both cords by drawing a circle around them that cuts thru the cords, and identify all forces acting.

 

[m2003]

Your approach is correct. The tension force in the rope must be equal to the force of gravity acting on the person and the bucket in order for her to raise herself at constant speed. However, your calculation for the force of gravity is incorrect. The correct equation for force of gravity is Fgravity = mg, where g is the acceleration due to gravity (9.8 m/s^2). Therefore, the correct calculation would be Fgravity = (63 kg)(9.8 m/s^2) = 617.4 N. This is the amount of force that the person must pull downward on the rope in order to raise herself at constant speed.