# Math Help - Average velocity question

1. ## Average velocity question

1. On a rainy day, you are travelling in a car at 20m/s when you suddenly apply the brakes - at, say, t = 0 seconds. The distance that you skid after braking is given by the function x(t) = 20t - t^2, where x is measured in meters.

a) Find the average velocity of your car over the following intervals of time.

i) between 4 and 5 seconds
ii) between 4 and 4.1 seconds
iii) between 4 and 4.0001 seconds

b) Using your answers above estimate the instantaneous velocity of the skidding car at 4 seconds after you braked.

Will I use this formula to figure out part a ?

(f(x+h) - f(x))/h. If so will the information "20m/s" be useless then?

2. Originally Posted by letzdiscuss
1. On a rainy day, you are travelling in a car at 20m/s when you suddenly apply the brakes - at, say, t = 0 seconds. The distance that you skid after braking is given by the function x(t) = 20t - t^2, where x is measured in meters.

a) Find the average velocity of your car over the following intervals of time.

i) between 4 and 5 seconds
ii) between 4 and 4.1 seconds
iii) between 4 and 4.0001 seconds

b) Using your answers above estimate the instantaneous velocity of the skidding car at 4 seconds after you braked.

Will I use this formula to figure out part a ?

(f(x+h) - f(x))/h. If so will the information "20m/s" be useless then?
Yes, and the 20 m/s is built into the skid distance formula, so you do not need it explicitly.

CB