Question

A block of mass M is placed on a rough floor of a lift. The coefficient of friction between the block and the floor is μ. When the lift falls freely, the block is pulled horizontally on the floor. What will be the force of friction

• A. μ Mg
• B. μ Mg/2
• C. 2μ Mg
• D. None of these

Answer 1

Answer: (D)

None of these

Answer 2

When the lift moves down ward with acceleration 'a' then effective acceleration due to gravity

g' = g – a

$\therefore g ^ { \prime } = g - g = 0$ [As the lift falls freely, so a = g]

So force of friction $= \mu m g ^ { \prime } = 0$