A car whose engine is turned off is initially parked and is uniformly accelerated

at 2 m/s2 to a speed of 10 m/s. Which speed interval requires more force to

reach this speed, and why? Assume real-world friction exists between the tires

of the car and the road.

A) 0 m/s - 5 m/s because it initially requires more force to overcome static

friction

B) 5 m/s - 10 m/s because energy is exponentially related to speed

C) Both speed intervals require the same amount of force

D) 5 m/s - 10 m/s because kinetic friction is higher than static friction

Click to reveal answer

Correct answer: A. Assuming friction exists between the tires and

the road, we need to account for the difference between static and kinetic friction

since the car starts at rest. Static friction is typically greater than kinetic friction

(meaning it takes more force to begin moving an object against friction before the

frictional force decreases). This means that the initial velocity interval from 0 m/s -

5 m/s requires more force because it includes overcoming static friction.

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Day 20 MCAT Practice Question