Physics, asked by abhishek6883, 3 months ago

b) An object of mass 40 kg is been acted upon by a force that changes its velocity from 30 km/h to 25 km/h
How much work is done by the force? Is the work done negative or positive?​

Answers

Answered by rsagnik437
7

Given:-

→ Mass of the body = 40kg

→ Initial velocity of the body = 30km/h

→ Final velocity of the body = 25km/h

To find:-

→ Work done by the force and is it

positive or negative.

Solution:-

Firstly, let's convert the initial and final velocity of the body from km/h to m/s.

=> 1 km/h = 5/18 m/s

=> 30km/h = 5/18×30

=> 8.33 m/s (u)

=> 25km/h = 5/18×25

=> 6.94 m/s (v)

_____________________________

Now, we know that :-

Work done = Change in Kinetic energy

=> W = Final K.E. - Initial K.E.

=> W = 1/2mv² - 1/2mu²

=> W = m/2[v² - u²]

By substituting values, we get :-

=> W = 40/2[(6.94)² - (8.33)²]

=> W = 20[48.1636 - 69.3889]

=> W = 20[-21.2253]

=> W = - 424.506 J

So, we can conclude that as the velocity of the object had decreased with time, hence it was acted upon by a retarding force.

Thus, work done by the force is negative.

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