Problem 36P

A 15-cm-radius air duct is used to replenish the air of a room 9.2 m × 5.0 m × 4.5 m every 16 min. How fast does air flow in the duct?

ANSWER:Initial speed of the hockey puck was 5 m/s.Kinetic friction coefficient between ice and puck is, = 0.05. KThe normal reaction the puck will get is, N = mg = 9.8 × mThe frictional force is, F = × N = 0.05 × 9.8 × m = 0.49 × m = 0.50 × m (approximately) KWe know by the definition of work, W = F| || | = 0.50 × m × S × cos 0 = 0.50 × m × S -------------------(1)STEP 2:-The velocity of the hockey puck was 5 m/s, so it’s kinetic energy will be, K.E = 1/2 mv = 1/2 × m × 5 = 12.5 × m---------------------(2)But the kinetic energy has to be same with the work done by the frictional force. So, bycomparing equation (1) and (2), K.E = 12.5 × m = W = 0.50 × m × S S = 12.5 / 0.50 = 25meters.CONCLUSION:Before getting stopped, the puck will travel 25 meters.