KVPY SX SB Exam 2015 Question Paper

Question : 21 of 120

Marks: +1, -0

PHYSICS

A small box resting on one edge of the table is struck in such a way that it slides off the other edge, 1 m away, after 2 seconds. The coefficient of kinetic friction between the box and the table -

must be less than 0.05
must be exactly zero
must be more than 0.05
must be exactly 0.05

Validate

Solution:

Velocity after time t

v = v_0-µgt

v ≥ 0 ⇒ v_0 ≥µgt

….(i)
Displacement in time ‘t’

∆ X=v_0t -1/2µgt^2

1 = 2v_0 -1/2µg(2)^2

2v_0 = (1 + 2µg)

v_0 = (1/2 + µg)

….(ii)

1/2+µg>µgt\;\;\;(t = 2 sec)

1/2+µg>2µg

µg<1/2

µ<1/{2g}

µ < 0.05

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