Question

A solid cylinder is given a velocity $v_{0}$ and an angular speed $\omega _{0}$ in the anticlockwise direction and then it is placed gently on a very long rough plank (initially at rest) as shown in the figure. Then, choose the incorrect statement:

• A. the friction force on the disc is in the backward direction till pure rolling starts
• B. the friction force between the disc and the plank is kinetic in nature till pure rolling starts
• C. the total momentum of system (disc and plank) is conserved
• D. the angular momentum of the disc about any point on the horizontal surface remains conserved

Answer 1

Answer: (D)

Initial velocity of point of contact of disc is in forward direction.
Hence friction is in backward direction and kinetic in nature.
Net force on the system is zero. So momentum is conserved.