# A little help please?

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Spotting a police car, you brake your Porsche from a speed of 100 km/h

to a speed of 80.0 km/h during a displacement of 88.0 m, at a constant acceleration.

a. What is that acceleration?

b. How much time is required for the given decrease in speed?

Spotting a police car, you brake your Porsche from a speed of 100 km/h

to a speed of 80.0 km/h during a displacement of 88.0 m, at a constant acceleration.

a. What is that acceleration?

b. How much time is required for the given decrease in speed?

##### 1 Answer

a.

b.

#### Explanation:

We have velocity in km/hr and displacement in m. Since we have to make a unit conversion, might as well do it so it will yield the answer in the normal (SI) units for acceleration.

a. Using the formula of motion

#(22.22 m/s)^2 = (27.78 m/s)^2 + 2*a*88.0 m

b. Since the acceleration was constant, we can use the average velocity, and the distance to determine the time.

As a double-check, if we convert

I hope this helps,

Steve