A person shoveling snow from a sidewalk is metabolizing food at a rate of 830 W.

Question

A person shoveling snow from a sidewalk is metabolizing food at a rate of 830 W.
Using data from table 7.2,

1. Calculate the power output during this activity.

2. How long will it take for this person to lift 3300 kg of snow to a height of 1.2m ?

3. How much heat will the person generate during this process?

Table 7.2 Efficiency of the Human Body and Mechanical Devices Activityldevice Efficiency Cycling and climbing 20 2 Swimming, surface 4 Swimming, submerged Shoveling Weightlifting Steam engine 17 Gasoline engine 30 Diesel engine 35 Nuclear power plant 35 Coal power plant 42 Electric motor 98 Compact fluorescent light 20 Gas heater (residential) 90 Solar cell 10

Explanation / Answer

Taking efficiency at 3% the power output is =830*(3/100)=24.9 w

2.Let the time take is t

then (24.9)*t=mgh=nett work done=3300*1.2*9.8=38808 J

24.9 w is the effective power

t=38808/24.9=1558.55 s

=25.97 mins

3. rest of the energy is dissipated as heat

that is 97 % of total energy

(830*1558.55)J*0.97=1254788.60J is dissipated as heat

i.e 1254.78 kJ of energy is dissipated as heat/loss

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