Question:
Compare the power at which each of the following is moving upwards against the force of gravity? (given $g$ $=10 \mathrm{~ms}^{-2}$ )
1. a butterfly of mass $1.0 \mathrm{~g}$ that flies upward at a rate of $0.5 \mathrm{~m} \mathrm{~s}^{-1}$.
2. a $250 \mathrm{~g}$ squirrel climbing up on a tree at a rate of $0.5 \mathrm{~m} \mathrm{~s}^{-1}$.
Solution:
1. $P=F v=m g v=1 \times 10^{-3} \times 10 \times 0.5=5 \times 10^{-3} \mathrm{~W}$
2. $P=F v=m g=250 \times 10^{-3} \times 10 \times 0.5=1.25 \mathrm{~W} .$