Find the speed of sound in air at 0 ∘c ( 1100 ft/s ) in mph.

We are already given the magnitude of the speed which is 1,100 ft/s. All we have to do is convert this to miles per hour. So, we have to know the conversion factor. Note that there are 5,280 ft in 1 mile, and 3,600 s in 1 hr. The solution is as follows:

(1,100 ft/s)(1 mile/5,280 ft)(3,600 s/1 h) = 750 mph

F = M*A 

200N*10KG is 2000 newtons

so 2000 newton's is the normal force that is being exerted on the block