Well, the density of the water is

so i believe that is what the question is asking for :)
Answer:
work = 1728
Power = 134
Explaination:
by using the formula,
Work(W)= Force(F)×Distance(D)
<h2>
and</h2>
Power(P)= Work(W)/Time taken(T)
Answer:
At an angle of 
Explanation:
Assume the river flows from East to West so for the swimmer to cross across it, assume he crosses it from West to East.
The resultant speed will be given by

Since work is the change in kinetic energy, the efficiency of a machine can be stated as the percentage of the output work divided by the input work minus the work lost from to friction and heat. Multiply Eff by 100% to get the efficiency percentage.
Periodic time is the time taken for one complete oscillation by a body in circular motion. In this case the merry-go round takes 2 minutes to cover 15 complete oscillations. 2 Minutes = 120 seconds
Hence, 15 oscillations takes 120 secs
thus 1 oscillation takes 120/15 = 8 seconds
therefore the period of the merry-go-round = 8 seconds