Question

PLEASE HELP!!!!

Compared to driving at 20 mph, about how much longer will it take for you to stop at 60 mph?
about nine times as far
about six times as far
about twice as far

Answer 1

9 times

Step-by-step explanation:

Answer 2

The braking distance would be about nine times as long (assuming that acceleration during braking stays the same.)

Step-by-step explanation:

Let
`u` denote the initial velocity of the vehicle (
`20\; \text{mph}` or
`60\; \text{mph}`) and let
`v` denote the velocity of the vehicle after braking (
`0\; \text{mph}`). Let
`x` denote the braking distance.

Assume that the acceleration during braking are both constantly
`a` in both scenarios. The SUVAT equations would apply. In particular:

`\begin{aligned} x &= (v^(2) - u^(2))/(2\, a)\end{aligned}`.

Since
`v = 0` (the vehicle has completely stopped), the equation becomes
`x = (-u^(2)) / (2\, a)`.

Assuming that
`a` (braking acceleration) stays the same, the braking distance
`x` would be proportional to
`u^(2)`, the square of the initial velocity.

Hence, increasing the initial speed from
`20\; \text{mph}` to
`60\; \text{mph}` would increase the braking distance by a factor of
`3^(2) = 9`.