Question

reading & writing - part 2
a moving car experiences two kinds of drag that slow it down. friction drag is created as air rubs against the surface of the car. pressure drag is created as air is compressed in front of the car. it can be reduced by adjusting the shape of the car so that air flows around it more smoothly. fin - shaped strips called “spoilers” are attached to the backs of many cars to reduce the overall drag they create and so help them go faster. although spoilers increase friction drag by increasing the car’s surface area,
which choice most logically completes the text?
a they perform better at higher speeds, since drag of both kinds increases with velocity.
b they reduce pressure drag by encouraging air to flow more smoothly around the back of the car.
c their streamlined aesthetic gives the impression of increased speed in competitive settings.
d friction drag can help cars move faster as long as pressure drag only reaches moderate levels.

Explanation:

The text discusses how spoilers are attached to cars to reduce overall drag and help them go faster, despite increasing friction - drag. The key is to explain how they still contribute to speed - increase, which is by reducing pressure drag. Option B correctly states that spoilers reduce pressure drag by encouraging air to flow more smoothly around the back of the car. Option A is about performance at higher speeds in general, not specifically about spoilers. Option C focuses on the aesthetic aspect rather than the functional aspect of drag - reduction. Option D has an incorrect statement as friction drag generally slows cars down, not helps them move faster.

Answer:

B. they reduce pressure drag by encouraging air to flow more smoothly around the back of the car.