18 ) [TIF] A nozzle of inner radius 0.3 cm is attached to a garden hose of inner radius 1. 5 cm. If water is fbwing through the hose at I m/s , it is flowing through the nozzle at 25m/s , and the volume flow rate is 21.21 mals . 19 ) A very strong wind blowing across a roof top can cause a large pressure difference between the ain inside and outside of the house . Under extreme conditions this effect can destroy the roof of a house. As an example, consider a 130 mply wind ( 1 mph = 0. 447 m/s) , blowing horizontally across a horizontal roof top of area 200 m 2 . What is the resulting force on the roof ? ( neglect the mof's thickness ) a ) 425 *123 N up wards b ) 405 x 10' N downwards C ) 810 x 10'N downwards d 2 x 10 7N upwards () none of the abovefor problems 16, 17 : A uniform steel rod of mass M and length Lis attached horizontally to the wall of a building . It is held in place by a joint at the interface with the wall, and a cable that is attached to the rod's and and to the wall a height L above the rod ( egnal to the rod 's length ) , see the figure , 16 ) The tension I in the cable equals a ) Mg 5 ) Mg c ) Ma d ) 52 Mg e )2Ma 2 (Hint : use the rotational equilibrium condition? ) 17 ) The wall exerts an upwards force fy on the rod and a horizontal force fx in the rod, given by Fy = fx =+My/ 220) In order to be suspended under water, fish use a bladder that they can expand or deflate . This varies their average density. A fish has volume and a density of 1 100 kg/m3 when It's bladder is fully deflated . Expanding its bladder so that it is suspended in fresh water changes its Volume by OV . The percentage change in it's volume , DV x 1008 , equals a ) - 10% b) - 5 3 c ) 0 % d ) + 5 3 e) + 102