# Homework Help: Weight of the roof

1. Nov 6, 2008

### itryphysics

1. The problem statement, all variables and given/known data

A 190 km/h wind blowing over the flat roof of a house causes the roof to lift off the house.
If the house is 6.5m x 15m in size, estimate the weight of the roof. Assume the roof is not nailed down.

2. Relevant equations

Bernoulli's equation : P1 + 1/2pv^2 +pgy = P2 + 1/2pv^2 + pgy

3. The attempt at a solution

i reduced the equation down to 1/2pv^2 to get pressure which numerically was 1671.3 and then i multiplied that by the area which i calculated to be 97.5 m^2, to get the force.

I was clueless on how to approach this problem, but im even more confused now. please help.

2. Nov 7, 2008

### HallsofIvy

You are done, aren't you? The problem asked for the weight of the roof. In order to lift something, you must apply a force (at least) equal to its weight. If the force you calculated was just enough to lift the roof, then that is the weight of the roof!