Question

1. Rubbing your hands together warms them by converting work into thermal energy. If a woman rubs her hands back and forth for a total of 16 rubs, at a distance of 7.50 cm per rub, and with a frictional force of 40.0 N, what is the temperature increase in degrees Celsius? The mass of tissue warmed is only 0.100 kg, mostly in the palms and fingers. ____ °C.

Answer 1

Given:

The frictional force, F = 40.0 N

Number of rubs, N= 16

Distance covered per rub, d = 7.50 cm = 0.075 m

Total distance covered in 16 rubs, D = 0.075 × 16 = 1.20 m

mass of the tissues warmed, m = 0.100 kg

Now,

Work done, W = Force × Displacement

W = 40N × 1.20m = 48 J

Now,

Work done is the change in heat

W = ΔQ = 48 J

also,

ΔQ = mCΔT

where, C is the specific heat

for human tissue, C = 3500 J/kg°C

thus,

48 J = 0.1 × 3500 × ΔT

ΔT= 48 / (350)

or

ΔT = 0.1371°C

the temperature increase in degrees Celsius is = 0.1371°C

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