You are a member of a production crew filming a nature explorer in the rocky mountains. the explorer needs to swim across a river to his campsite. by watching debris flowing down the river, you estimate that the stream is flowing at 0.677 m / s. in still water, he can swim at 0.763 m / s. at what angle, less than 90°, with respect to the shoreline would you advise him to swim to travel directly across the stream to his campfire?

If we wish to cross the river in such a way that we reach directly opposite to the bank then in that case the velocity parallel to the flow of river must be ZERO

So here the let say he start his motion at some angle "theta" with the shore

So the velocity opposite to the flow of river must be same as the velocity of river so that it will cancel out

now here we can say

given that

v = 0.763 m/s

now from above equation

now the angle is given as

note: the given question is incomplete.

complete question is given below.

which is an example of kinetic energy?

a. the energy stored in ethanol  

b. a hockey puck sliding across the ice  

c. a compressed spring  

d. a ball sitting at the top of a ramp

solution: the kinetic energy is the energy posses by the virtue of the motion of the object.

in the given options, a, c and d are the example of potential energy because it is the energy posses by the virtue of the rest of the object. but option b has the kinetic energy as the object is in motion.

hence, a hockey puck sliding across the ice   is the apex example of kinetic energy.

so, the option (b) a hockey puck sliding across the ice   is the correct option.