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 groundno workpositive work negative work(b) a person studyingno workpositive work negative work(c) a crane lifting a bucket of concreteno workpositive work negative work(d) the gravitational force on the bucket of concreteno workpositive work negative work(e) the leg muscles of a person in the act of sitting downno workpositive work negative work
Question
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 groundno workpositive work negative work(b) a person studyingno workpositive work negative work(c) a crane lifting a bucket of concreteno workpositive work negative work(d) the gravitational force on the bucket of concreteno workpositive work negative work(e) the leg muscles of a person in the act of sitting downno workpositive work negative work
Solution
(a) A chicken scratching the ground: Positive work. The chicken is applying a force to the ground and moving it, which is the definition of work in physics.
(b) A person studying: No work. While studying requires mental effort, it does not involve moving an object with a force, so it does not count as work in the physical sense.
(c) A crane lifting a bucket of concrete: Positive work. The crane is applying an upward force to the bucket and moving it upward, which is work.
(d) The gravitational force on the bucket of concrete: Negative work. Gravity is pulling the bucket downward, which is the opposite direction of the force applied by the crane. This is considered negative work.
(e) The leg muscles of a person in the act of sitting down: Negative work. The person's muscles are exerting a force to control the descent, but the movement (sitting down) is in the opposite direction of the force, so this is considered negative work.
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