[Ali73]

1.) A typical flying insect applies an average force equal to twice its weight during each downward stroke while hovering. Take the mass of the insect to be 10 g, and assume the wings move an average downward distance of 1.0 cm during each stroke.

-Assuming 100 downward strokes per second, estimate the average power output of the insect.
Express your answer using two significant figures.

2.) The aircraft carrier John F. Kennedy has mass of 7.4x10^7 kg. When its engines are developing their full power of 280000 hp, the John F. Kennedy travels at its top speed of 35 knots (65m/h).

-If 70% of the power output of the engines is applied to pushing the ship through the water, what is the magnitude of the force of water resistance that opposes the carrier's motion at this speed?
Express your answer using two significant figures.

[jcaron2]

1) The average power (in watts) is the total energy (in Joules) consumed in 1 second.

The energy consumed is equal to the amount of work done. Work = force * distance. How much force does the insect apply during each downward stroke? If one downward stroke is a distance of 0.01 m (1 cm), what's the total downward distance the wing travels in one second?

2) Since the ship is moving at a steady speed (not accelerating) that means the sum of the forces is zero, so the force of the engine propelling the ship forward is exactly equal (and opposite in direction) to the force of the water resistance, so you really just need to calculate the force that the engine is supplying.

They tell you how much power is consumed pushing the ship forward. If you convert that power from HP to watts, that will be the same as the number of Joules of energy used in 1 second to push the ship forward. The energy consumed in 1 second is the same as the work done in 1 second, which is equal to force * distance. So you just have to calculate the distance the ship will travel in one second, and (since you know how much work was done) you can solve for the force.