Question

An engine pumps water through a hose pipe. Water passes through the pipe and leaves it with a velocity of $2m/s$. The mass per unit length of water in the pipe is $100kg/m$. What is the power of the engine (in W)?

• A. $100$
  
• B. $200$
  
• C. $400$
  
• D. $800$
  

Answer 1

The correct option is C $400$

Amount of water flowing per second = $\frac{m}{time}$ = $\frac{m}{l}$ $\ast$ $\frac{l}{t}$ = ( $\frac{m}{l}$)v

Kinetic energy of water flowing per second = power = $\frac{1}{2}$( $\frac{m}{l}$)v${}^3$

= $\frac{1}{2}$ $\ast$100 $\ast$ 8 = 400W