Question

Your older brother is driving at 35 km/h when the road suddenly descends 15 m into a valley. He takes his foot off the accelerator and coasts down the hill. Just as he reaches the bottom you see a policeman hiding behind the speed limit sign that reads "70 km/h." Is your brother going to get a speeding ticket?

Answer 1

Yes

Step-by-step explanation:

m = Mass of car

g = Acceleration due to gravity = 9.81 m/s²

u = Initial velocity = 35 km/h

v = Final velocity

h = Altitude = 15 m

Here, the energy is conserved

`KE=PE\\\Rightarrow (1)/(2)m(v^2-u^2)=mgh\\\Rightarrow v=√(2gh+u^2)\\\Rightarrow v=\sqrt{2* 9.81* 15+\left((35)/(3.6)\right)^2}\\\Rightarrow v=17.15517\ m/s`

Converting to km/h

`1\ m/s=3.6\ km/h`

`\\\Rightarrow 19.71855=19.71855* 3.6\ km/h=70.98678\ km/h`

The speed of the car is 70.98678 km/h is greater than 70 km/h.

Hence, a speeding ticket will be given