One or more options correct
A small block rests on a horizontal turntable at a distance from its axis; the coefficient of static friction between block and table is . The turntable is started from rest and speeds up with constant angular acceleration . Take . Which of the following is/are correct?
- A. The block starts to slip at .
- B. At the instant just before slipping, the friction force on the block makes an angle of about with the line joining the block to the axis.
- C. The block slips only after the turntable has completed at least one full revolution.
- D. The speed of the block just before it starts to slip is .
Show answer and solution
Answer: A, B, D
The block has tangential acceleration and centripetal acceleration , both supplied by static friction, so . Slipping begins when this equals : , hence , . Then : (A) is correct. The friction components are (tangential) and (towards the axis), so the angle with the radial line satisfies , : (B) is correct. The angle turned is , which is only about revolution, so (C) is incorrect. The speed is : (D) is correct.
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