6-44. In a biceps curl, a weightlifter lifts a mass of 15 kg a vertical distance of 66 cm.
(a) How much work is done by gravity on the mass?
(b) Neglecting any accelerations, how much work is done by the weightlifter on the mass?
(c) By how much does the gravitational potential energy of the mass increase?

 

 
ACCUMULATED SOLUTION

 
 
 
 
 
 
 

(a) Fgd = (15 kg)(-9.8 m/s2)(0.66 m) = -97 J
 
 


 
Correct!
Since mg and d are in opposite directions then one of them is negative. If +y is up then the gravitational force is -mg.
This is the answer to part (a).

 
 

The applied force is:

(A)Fapp = mg

(B)Fapp = -mg

(C)Fapp = 0