Help me PLEASE with this maths question???? 10 POINTS FOR BEST ANSWER!!

Here are the formulae to work out the thinking distance and the braking distance
for a car travelling at V miles per hour.
Thinking distance = V feet
Braking distance = Vsquared divided by 20 feet

A different car is travelling so that its braking distance is 125 feet.
How fast is the car travelling?


This is the link to the actual question(scroll down to question 12) http://www.emaths.co.uk/SAT%20PAPERS/KS3%20SAT%20Papers/Mathematics%20KS3%20SAT%20Papers/Mathematics%20KS3%20SAT%202009/57P2.pdf


can u show me how to work it out aswell please.
Thanks x

Okay i think i know how to do this...

Thinking distance = V feet Braking distance = V^2/20 feet

a.A car is travelling at 70 miles per hour.
What is the total stopping distance for this car?

so for this answer you just need to plug in the speed of the car

thinking distance= 70 feet braking distance= (70)^2/20

70 + 4900/2

70 + 2450 = 2520

The total stopping distance for a car going 70 mph is 2520 feet.

b.A different car is travelling so that its braking distance is 125 feet.
How fast is the car travelling?

In this question they are telling you to work backwards so now you need to find V or speed at which the car is traveling

125= V^2/20

multiply both sides by 20

20(125)=V^2

2500=V^2

now you take the square root of both sides

√2500= √V^2

50=V

So then you have the answer: The car is traveling 50 mph when the braking distance is 125 ft.

Hope that helps :)

(a) The thinking distance = speed of the car in feet. The question gives an example: thinking distance for a 30 mph car is 30 feet. Hence for the car traveling at 70 mph, the thinking distance = 70 feet.

Braking distance = V square divided by 20 = 70 ^ 2 / 20 = 4900 / 20 = 490 / 2 = 245 feet.