A75-kg sprinter accelerates from rest to a speed of 11.0 m/s in 5.0 a) calculate the mechanical work done by the sprinter during this time. i know w=0.5mv^2 = 4538 j . b)calculate the average power the sprinter must generate. p=w/t= 908w. c) if the sprinter converts food energy to mechanical energy with an efficiency of 25%, at what average rate is he burning calories? .

A. Work = KE = 0.5mv²
   Substituting the known values,
                                  KE = 0.5(75 kg)(11 m/s)² = 4537.5 J
b. Power = W / t. Substituting,
                                   P = 4537.5 J / 5 s = 907.5 W
c. Only 25% is absorbed. So, the sprinter only absorbed 226.875 J per second which is equal to 54.20 calories per second. 

The boat's velocity relative to the riverbank can be resolved into two components. the component going north is 2.7 m/s and the component going west is 1.2 m/s.we add these two vectors and then find the magnitude of the resultant to get the speed.the magnitude of the resultant vector from adding can be obtained by the pythagorean theorem.    to two significant figures, the boat's speed relative to the riverbank is 3.0 m/s.