Manipal Entrance Test 2015 Physics Paper

Net pulling force = 2g - 1g = 10 N
Mass being pulled = 2 + 1 = 3 kg
∴ Acceleration of the system is a =

10

3

m∕s2
∴ Velocity of both the blocks at t =1 s will be
v0=at=(

10

3

)(1)=

10

3

m∕s
Now at this moment, velocity of 2‌kg becomes zero, while that of 1‌kg block is 10m∕s upwards. Hence, string becomes tight again when displacement of 1‌kg block = displacement of 2‌kg block.
⇒v0t−

1

2

gt2 =

1

2

gt2
⇒t=

v0

g

=

10 3

10

=

1

3

s