First slide

Fluid dynamics

Question

The outboard motor of a small boat has a propeller of diameter 200 mm. When the boat is at rest, the propeller sends back a stream of water at a speed of 10 m/s. One-half of the work that is being done by the motor is transferred to this water as kinetic energy. The power output of the motor is ( density of water is 1000 kg/m³) :

Easy

A

1.25 kW
B

6.50 kW
C

15.7 kW
D

31.4 kW

Solution

$Power = \frac{1}{2} Fu = \frac{1}{2} ({ρAu}^{2}) \times u = \frac{1}{2} \times (10^{3}) \times π {(0.1)}^{2} \times {(10)}^{3} = 31.4 kW$

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