In the given arrangement, there is no friction any where. Pulley and string are ideal. Acceleration due to gravity is 10 m / s 2 downward. Find out total work done by gravity in 2 sec, if system start

Question

In the given arrangement, there is no friction any where. Pulley and string are ideal. Acceleration due to gravity is 10 m / s 2 downward. Find out total work done by gravity in 2 sec, if system starts from rest.

TestHub · Accepted Answer

Only the hanging block moves vertically under gravity.

Both blocks have the same acceleration.

$a = \frac{4 g}{4 + 4} = 5 m/ s^{2}$

In 2 s, the hanging block descends

$s = \frac{1}{2} a t^{2}$

$s = \frac{1}{2} (5) (2)^{2} = 10 m$

Work done by gravity on the hanging block:

$W_{g} = m g s$

$W_{g} = (4) (10) (10)$

$W_{g} = 400 J$

Option B.

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