A gale blows over a house. The force due to the

gale on the roof is

(a) in the direction of gale

(b) upward (c) downward

(d) in the direction of gale

i feel

as the gale moves over a roof it will create a low press region than one below the roof thus a force will be upwards

another factor is the force exerted by gale on the roof due to its loss in momentum that will act down wards

so it will depend upon the resultant

good question

Obviously answer must be (b)upward.

This is based on Bernoulli's theorem.

Above the roof the wind blows at high speed than below the roof creating a low pressure region above the roof and high pressure below the roof.As a result a force is developed from down the roof(i.e. from high pressure region to low pressure region) by the movement of the wind pushing it upwards.

This is the reason for blowing away of roof tops during wind storms.

Also this principle is used in Lifting of Aeroplane.

wanted to add one thing more the momentum reason will only apply if the roof is slanted

if roof is parallel no momentum loss occurs