Acceleration word problems

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 ?

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 = 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.

Challenging and interesting acceleration word problems

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 = 1 foot/s²
Your brother's acceleration = 1 foot/s²

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?