Discuss whether any work is being done by each of the following agents and, if so, whether the work is positive or negative: (a) a chicken scratching the ground, (b) a person studying, (c) a crane lifting a bucket of concrete, (d) the gravitational force on the bucket in part (c), and (e) the leg muscles of a person in the act of sitting down.

Explanation

a. Positive work is done by the chicken on the dirt.
b. The person does no work on anything in the environment. Perhaps some extra chemical energy goes thorugh energy transmitted electrically and is converted into internal energy in his brain, but it would be very hard to quantify "extra".
c. Positive work is done by crane on bucket in lifting it from ground.
d. Gravitational force will do negative work because the force is opposite to displacement.
e. When we do any activity our forces in muscles will do some positive work.