Two Practice Problems (MCQ) on Friction

Posts on friction were published on this site on 12^th August 2006, 7^th May 2007, 23^rd May 2007 and 1^st June 2007. You can access these posts easily by clicking on the label ‘friction’ below this post or on the side of this page. It will be beneficial for you to go through those posts before trying the practice problems given below:

(1) A block of mass ‘M’ equal to 1 kg is resting on a frictionless horizontal surface. Another block of mass ‘m’ equal to 0.2 kg is resting on the top surface of the 1 kg block. The coefficient of friction between the two blocks is 0.2. The motion of the 1 kg block is controlled by a light spring of force constant 24 Nm^–1 arranged as shown in the figure. What is the maximum possible amplitude of oscillation of the blocks (together) so that the upper block does not slip relative to the lower block? (g = 10 ms^–2)

(a) 2 cm (b) 5 cm (c) 10 cm (d) 20 cm (e)50cm

(2) A metallic cube takes ‘t’ seconds to slide down a smooth inclined plane of angle 45º. When the inclined plane is made rough, the block takes nt seconds to slide down. The coefficient of friction between the block and the rough incline is

(a) 1/n (b) 1 – (1/n) (c) 1 – (1/n²) (d) (1/n²) (e) 1 + (1/n²)

Try to solve the above problems. I’ll be back with the solution shortly.