The apparatus shown in the figure below was used by Joule to measure the mechani

Question

The apparatus shown in the figure below was used by Joule to measure the mechanical equivalent of heat. Work is done on the water by a rotating paddle wheel, which is driven by two blocks falling at a constant speed. The temperature of the stirred water increases due to friction between the water and the paddles. If the energy lost in the bearings and through the walls is neglected, then the loss in potential energy associated with the blocks equals the work done by the paddle wheel on the water. If each block has a mass of 1.45 kg and the insulated tank is filled with 200 g of water, what is the increase in temperature of the water after the blocks fall through a distance of 2.65 m?

Explanation / Answer

ANSWER

From theory we know that,

2*mb*g*h = mw*Cd*dT

where,

mb = mass block = 1.45 kg

mw = mass water = 200 g

Cd = especific heat of water = 4.186 J/g ºC

h = distance = 2.65 m

g = gravity = 9.8 m/s2

Thus,

2 * 1.45 * 9.8 * 2.65 = 200 * 4.186 * dT

dT = 0.08996 ºC ANS.

Regards!!!

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