Three part weightlifter question

[physicsgurl12]

Homework Statement

A weightlifter works out at the gym each day. Part of her routine is to lie on her back and lift a 40kg barbell straight up at a distance of .50m.
a. how much work does the weightlifter do to lift the barbell one time?
b. if the weightlifter does 20 reps a day what total energy does she expend on lifting? assume 25% efficency.
c. How many 400 calorie donuts can she eat a day to supply that energy.

Homework Equations

w=fd f=ma

The Attempt at a Solution

w=fd w=f*.50m
f=40kg*a ?/

 

[JHamm]

Use the work energy theorem, the barbell has zero velocity at both the top and bottom of the rep.

 

[I like Serena]

Your acceleration "a" is the acceleration of gravity: g=9.8 m/s2.
With what you already have you should be able to find the work w...