Two blocks of mass 1 kg & 2 kg are hanged from a light pulley and resting on a horizontal surface. A time varying force F = 4t N is acting on pulley in the direction shown. Time after which block will break off the surface will be –

• Correct answer
  A

  5
• B

  10
• C

  15
• D

  20

Solution

1 kg block
$N+F/2=10;$
$\Rightarrow F=2(10–N)$
Block 1 will leave
surface when N = 0
$\Rightarrow F=20\Rightarrow 5\sec$

Hence, the correct answer is option: 'A'.