An observer stands on a bridge over the M$42$ motorway at night. A police car travels effec tively directly towards the observer at a speed of $112$ kmh$1,$ with his horn sounding at a frequency of $250$ Hz$.($a$)$ Calculate the frequency heard by the observer. $2$ marks $($b$)$ The car$$s blue lights are flashing. Taking a typical value for the frequency of blue light, calculate the frequency of the light seen by the observer. $2$ marks $($c$)$ The car approaches a tunnel in a vertical cliff. The horn$$s sound reflects off the cliff face and the echo is heard by the driver. What frequency does the driver hear?