Static and kinetic friction, laws of friction, rolling friction
- There are two inclined surfaces of equal length (L) and same angle of inclination 45^° with the horizontal. One of them is rough and the other is perfectly smooth. A given body takes 2 times as much time to slide down on rough surface than on the smo… Answer: 4. 0.75 Key idea: for a fixed length L starting from rest, L=1/2 a t² , so t∝ 1/sqrt a . Smooth plane: a_s=gsin45^° . Rough plane: a... 1
- A horizontal force 10 N is applied to a block A as shown in figure. The mass of blocks A and B are 2 kg and 3 kg, respectively. The blocks slide over a frictionless surface. The force exerted by block A on block B is : Answer: 4. 6 N Key idea: Both blocks move together with the same acceleration. Find it first, then use it for block B. a=F/m_A+m_B=10/2+3=2... 1
- Calculate the maximum acceleration of a moving car so that a body lying on the floor of the car remains stationary. The coefficient of static friction between the body and the floor is 0.15 (g=10 m s^-2). Answer: 4. 1.5 mathrmm s⁻² The body stays at rest relative to the car only while the pseudo-force ma is balanced by static friction, whose m... 1
- A block of mass 10 kg is in contact against the inner wall of a hollow cylindrical drum of radius 1 m. The coefficient of friction between the block and the inner wall of the cylinder is 0.1. The minimum angular velocity needed for the cylinder to ke… Answer: 3. 10 rad/s The wall's normal force supplies the centripetal force: N=mω²r . Friction balances weight: μ N=mg . μ mω²r=mg⇒ω=√(g/μ r)... 1
- Which one of the following statements is incorrect ? Answer: 4. Coefficient of sliding friction has dimensions of length. Check each statement. Rolling friction is smaller than sliding friction... 1