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.

Answer:

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

Mass of butterfly (mb) = 1 g = 10-3 kg

Speed (vb) = 0.5 ms-1

Force of gravity on butterfly (Fh) = mb × g

Fh = 10-3 x 10 = 10-2 N

Power (Pb) = Fb x vb

Pb= 10-2 N x 0.5 m s-1

Pb = 0.005 W

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

Mass of squirrel (ms) = 250 g = 0.25 kg

Speed (vs) = 0.5 m s-1

Force of gravity on squirrel,

Fs = ms × g

Fs = 0.25 x 10

Fs = 2.5 N

Power (Ps) = Fs × vs

Ps = 2.5 N x 0.5 m s-1

Ps = 1.25 W

Hence, the squirrel exerts more power in climbing than a butterfly exerts in flying at the same rate.

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