Question

Body of mass 3kg is dragged on horizontal surface with constant speed of 2 m/s. If the coefficient of friction between body and surface is 0.2, find heat generated in 10 sec. *
30 Cal
118 Cal
117.6 Cal
28 Cal

Answer 1

☆Concept:

》Here,we see that object is being dragged with constant velocity, that means its has zero acceleration, which further means the net force on object is zero.

》As the object is in motion, kinetic friction will be acting with constant magnitude, which is achieved after crossing the limiting value.

》work of friction will be loss in the form of heat.

☆Solution:

Kindly see the figure in attached image!

Net Work Done = 0 (as net force is zero)

$\rightarrow\rm W_{ext} - W_{friction} = 0$

$\rightarrow\rm W_{ext} = W_{friction}$

$\implies\rm W_{friction} = Force\times displacement$

$\implies\rm W_{friction} = \mu mg \times 20$

$\implies\rm W_{friction} = (0.2\times 3\times 10)\times 20$

$\implies\rm W_{friction} = 6\times 20$

$\implies\bf W_{friction} = 120 Joules.$

$\implies\rm W_{friction} = \dfrac{120}{4.2} cal$

$\implies\bf W_{friction} \approx 28 cal$

$\boxed{\bf Heat\;generated = 28 cal}$

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▪︎note:

• Here, the net work is '0', and still the object is doing displacement.
• Because the work done by ext. is the cause of its displacement, and the energy applied here is same which is lost as heat by friction; that's why net work is zero
• Here the work is synonym to the energy applied in the system.