Question

Figure shows a block of mass m resting on a plank of mass M, placed on a smooth horizontal surface The coefficient of friction between the block and plank is u. A horizontal force F is applied on the plank which varies with time t as F = kt (k is a positive constant). Select the correct alternative.

1) After time t = ug(M + m)/k, relative motion between block and plank starts

(2) Friction force between the block and plank remains constant after t = ug(M + m)/k
till the contact between two is lost
(3) Contact force between plank and ground increases with time

(4) Block will never move relative to the plank​

Answer 1

Answer:

option 2

Step-by-step explanation:

As the force is applied to the plank and the block is resting on the plank.Thus, mass of the block and mass of the planck are now considered as together one.

Also, the force varies with the time here. Hence, the correct answer is the second option.

Answer 2

Answer:

(2) Friction force between the block and plank remains constant after

t = ug (M + m)/k till the contact between the two is lost.

Step-by-step explanation:

• Friction force is the force that resists the sliding or rolling of one solid object over another.

• When force is applied to the plank and the block is resting on the plank. The mass of the block and the mass of the plank are now considered as together.                      

•  Also the force varies with the time here. Hence, the correct answer is (2) Friction force between the block and plank remains constant after
• t = ug (M + m)/k till the contact between the two is lost.