I don't get this Algebra Problem - Please HELP!?

Question

You don't need to give me the complete answer, just help explain the concept/the steps to do it.

The problem: That friend that was going 70 hit the brakes immediately after passing the speed trap. Braking distance directly with speed. If a car going 20 mph takes 80 feet to stop, write and graph an equation that shows braking distance versus speed and find out how long it took your friends to stop the car.

Answer 1

Well... the easy part is the answer. It took your friends 280ft to stop their veh. The tricky part is the graph. If the car going 20 mph takes 80 ft to stop, and it's directly proportionate to the graph, you can create a graph where the x-axis is the number of ft, easiest if starting at 0 and counting by 50's, and the y-axis is mph, starting at 0 and counting by 20's.

20mph 70 mph
---------- = -----------
80 ft X ft

Solve for x, and connect the dots. The first x is where 20 mph and 80 ft intersect, the second x is where 70 mph and 280 ft
intersect.

And x = 280 ft.

Answer 2

i may be wrong, it's been some time since i've done anything like this, but i think you first evaluate the second car.....

going 20mph it takes 80 feet to stop. so, for every 20 miles per hour, it takes 80 feet to stop. you can simplify it down to 2 mph - 8 feet and then 1mph - 4 feet. you could let x be speed and y be distance.
y= 4x would be the equation for the graph.

now just do some math to figure out how far it would take a car going 70 to stop.



like i said, i could be wrong....it's happened before.

Answer 3

ok.. since you are negating any other factors it is a simple proportion

if 20 mph take 80 feet what doees 70mph

20/80 = 70/x

can you take it from there????