This problem asks about how the **acceleration** of car could be increased from 8.40 mi/h·s depending on changes to the **net force applied** and the car's **mass**.

Anytime we have a problem asking about **force**, **mass**, and **acceleration** (and *only* those quantities), we'll use **Newton's 2nd Law**, often written as

$\overline{){\mathbf{\sum}}{\mathit{F}}{\mathbf{=}}{\mathit{m}}{\mathit{a}}}$

For some problems, we'll want it in a different form, solved for *a*:

$\overline{){\mathit{a}}{\mathbf{=}}\frac{\mathbf{\sum}\mathit{F}}{\mathit{m}}}$

Notice that acceleration is __directly proportional__ to **net ****force** and __inversely proportional__ to **mass**.

A young woman buys an inexpensive used car for stock car racing. It can attain highway speed with an acceleration of 8.40 mi/(h·s). By making changes to its engine, she can increase the net horizontal force on the car by 24.0%. With much less expense, she can remove material from the body of the car to decrease its mass by 24.0%.**(a)** Which of these two changes, if either, will result in the greater increase in the car’s acceleration?**(b)** If she makes both changes, what acceleration can she attain?

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What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the Newton's 3 Laws concept. If you need more Newton's 3 Laws practice, you can also practice Newton's 3 Laws practice problems.