A uniform disk with a mass of 115 kg and a radius of 1.4 m rotates initially wit

Question

A uniform disk with a mass of 115 kg and a radius of 1.4 m rotates initially with an angular speed of 1120 rev/min. A constant tangential force is applied at a radial distance of 0.6 m. What work must this force do to stop the wheel? I know you use change in kinetic energy to find the work and that this answer is 771,375 J, but why is the answer positive? I thought that the final kinetic energy would be 0 and you would subtract the initial kinetic energy, resulting in a negative answer. Does anyone have an explanation for this?

Explanation / Answer

We are finding the work donr BY the force, i.e we are finding the amount of energy expended by the force. hence we get the positive value. if we were looking for the change in the energy of the disk, we would get a negative value. now, loss in energy of the disk = work done by the force. ie the energy is going from the disk side to the force side of the equation, hence the work by the foce is positive.

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.