Consider a weightlifter holding a barbell motionless above his head.

(a) Is the sum of the forces exerted on the barbell zero? 

\((b)\) Is the weightlifter exerting a force on the barbell?

(c) If the weightlifter exerts a force, does this force do any work on the barbell?

(d) Does the energy of the barbell change?

(e) Are your answers to parts \(c\) and \(d\) consistent in light of the relationship between work and energy?