A wind with speed 40 m s - 1 blows parallel to the roof of a house. The area of the roof is 250 m 2 .…

A wind with speed 40 m s-1 blows parallel to the roof of a house. The area of the roof is 250 m2 . Assuming that the pressure inside the house is atmospheric pressure, the force exerted by the wind on the roof and the direction of the direction of the force will be : ρair =1.2 kg m-3 
  1. 4.8×105 N, downwards
  2. 4.8×105 N, upwards
  3. 2.4×105 N, upwards
  4. 2.4×105 N, downwards

Solution

By Bernoulli's equation,
P+12ρv2=P0+0
P0-P=12ρv2
F=12ρv2A
=12×1.2×402×250
=12×1.2×1600×250
=2.4×105 N, upwards ~

Asked in: NEET 2015 (Phase 1)

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