A block of negligible size and mass 2kg is placed above a plank of mass 4kg and length 16m as shown in figure. A force of 44N is applied on the lower block as shown in the figure. The ground is smooth, coefficient of friction between upper and lower block is 0.2. Find the time after which the upper block will fall over.

Options

A. (a)1s
B. (b)2s
C. (c)3s
D. (d)4s

Answer

B

Explanation

Fmax such that the blocks move together = `μ (M + m) g = 12N`
Hence, the block will slip over each other
`a_(2kg) = (4)/(2) = 2m//s^(2) a_(4kg) = (44 - 4)/(4) = 10 m//s^(2)`
relative to the lower block `implies a_(2kg) = 10 - 2 = 8m//s^(2)`
Hence, time for falling over `implies (1)/(2 8t^(2) = 16 implies t = 2s`