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Compare the power at which each of the following is moving upwards against the force of gravity? (given: g = 10 m s^{-2})

(i) a butterfly of mass 1.0 g  that flies upward at a rate of 0.5 m s^{-1}.

(ii) a 250 g squirrel climbing up on a tree at a rate of 0.5 m s^{-1}

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Solution.

Power of anything is defined as the rate of work done by that thing or energy supplied per unit time.
Mathematically, power is defined as the product of force and velocity.
Power = F v.
In lifting a body with constant speed, it has to apply force equal to his weight.
(i)For the Butterfly:
Mass of the butterfly:   m = 1 gram = 0.001 kg
Speed attained: V= 0.5 m s^{-1}
Force required:  F = mg = 0.01 N
By using the formula of power:
Power=0.01\times 0.5=5\times 10^{-3}watt
(ii)For the Squirrel:
Mass of the squirrel:      m =250 gram = 0.250 kg
Speed attained:     V = 0.5 m s–1
Force required:      F = mg = 2.5 N
By using the formula of power:
Power=2.5\times 0.5=1.25watt
 

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