Work AP Physics C Mechanics MCQ – Exam Style Questions etc.
Work AP Physics C Mechanics MCQ
Unit 3: Work, Energy, and Power
Weightage : 15-25%
Question
A spring has a force constant of 100 N/m and an unstretched length of 0.07 m. One end is attached to a post that is free to rotate in the center of a smooth table, as shown in the top view above. The other end is attached to a 1 kg disc moving in uniform circular motion on the table, which stretches the spring by 0.03 m. Friction is negligible.
What is the work done on the disc by the spring during one full circle?
A 0 J
B 94 J
C 186 J
D 314 J
E 628 J
Answer/Explanation
Ans:A
Question
How does the work required to accelerate a particle from 10 m/s to 20 m/s compare to that required to accelerate it from 20 m/s to 30 m/s ?
A It is less.
B It is the same.
C It is greater.
D It cannot be determined without knowing the magnitude of the force exerted on the particle.
E It cannot be determined without knowing the mass of the particle.
Answer/Explanation
Ans:A
Question
A spring has a force constant of 100 N/m and an unstretched length of 0.07 m. One end is attached to a post that is free to rotate in the center of a smooth table, as shown in the top view above. The other end is attached to a 1 kg disc moving in uniform circular motion on the table, which stretches the spring by 0.03 m. Friction is negligible. What is the work done on the disc by the spring during one full circle?
(A) 0 J (B) 94 J (C) 186 J (D) 314 J (E) 628 J
Answer/Explanation
Ans:A
Solution: In a circle at constant speed, the work done is zero since the Force is always perpendicular to the distance moved as you move incrementally around the circle
Question
A student holds one end of a string in a fixed position. A ball of mass 0.2 kg attached to the other end of the string moves in a horizontal circle of radius 0.5 m with a constant speed of 5 m/s. How much work is done on the ball by the string during each revolution?
(A) 0 J (B) 0.5 J (C) 1.0 J (D) 2π J (E) 5π J
Answer/Explanation
Ans:A
Solution: First, the speed is constant, so you expect (by the Work-Energy Theorem) that there isn’t any work. Beyond that, the definition of work for a constant force is F•∆r = F∆r cos θ. Since the force of the string is always radial, and the displacement tangential, the angle between these is 90º; the string can do no work. (It’s basically the same story as with magnetic fields acting on free charges; no work can be done by the magnetic field because the force is at right angles to the displacement.) All the given numbers are merely distracters.