Before you look at these acceleration word problems, you need to make sure you have mastered the topic about velocity.

**Problem #1:**

What is the acceleration of a motorcycle moving on a straight path when the speed goes from 0 to 70 miles per hour in 5 seconds ?

Acceleration =

change in velocity
time interval

The motorcycle goes from 0 to 70 m/h, so the change in speed is

70 - 0 = 70

It took the motorcycle 5 seconds to reach this velocity so the time interval is 5.

Plug these numbers into the formula.

Acceleration =

70
5

Acceleration = 14 m/h.s

Do you remember how to read the answer?

We read 14 m/h.s as 14 miles per hour-second.

In order words, each second, the speed increases by 14 miles per hour.

**Problem #2:**

What is the acceleration of a Honda Accord with a constant velocity of 50 km/h for 20 seconds? Does the car have a constant acceleration?

If the Honda has a constant velocity, this means that the speed is constant and the car is going on a straight path.

Because the speed is constant, the car is not accelerating.

The driver probably put the car on cruise control with a speed of 50 km/h for 20 seconds.

So a = 0.

There is a world of difference between constant acceleration and constant velocity.

Constant acceleration means that the speed is changing. However, it is changing by the same amount.

For example from 10 km/h to 20 km/h, then from 20 km/h to 30 km/h, etc.

The change in speed is always 10 km/h, so this is a constant acceleration.

Constant velocity on the other hand means that the speed is not changing!

Since the speed is not changing at all, the car does not have constant acceleration.

**Problem #3:**

You can speed up from 0 to 25 feet/s in 25 seconds and your brother can speed up from 0 to 6 feet/s in 6 seconds.

Who is faster?

Each second, your speed can increase by 1 foot/second.

If it is hard to see, you can always use the acceleration formula ****

Your acceleration =

25 feet/s
25 s

Your acceleration = 1 foot/s

Your brother's acceleration =

6 feet/s
6 s

Your brother's acceleration = 1 foot/s

Therefore, neither you nor your brother is faster.

**Problem #4: **Your turn! I will not solve this acceleration word problem for you.

Two cars are racing on the highway with the same constant acceleration of 10 miles per hour-second. They do this for 12 second.

Do you think the cars set their cruise control?

What was the instantaneous speed of the cars at the 5-second mark?

What is the highest instantaneous speed of the cars?