9:37 PM oo T-Mobile 71% session masteringphysics.com C PHYS 221 Winter 2016 TR H

Question

9:37 PM oo T-Mobile 71% session masteringphysics.com C PHYS 221 Winter 2016 TR Homework 9 Item 12 previous l 2 of 14 I next Item 12 The engine in an imaginary sports car can provide constant power to the wheels over a range of speeds from 0 to 70 miles per hour (mph). At full power, the car can accelerate from zero to 30.0 mph in time 1.50 s. Part A At full power, how long would it take for the car to accelerate from 0 to 60.0 mph Neglect friction and air resistance. Express your answer in seconds. 6.00 s mit Hints My Answer Give Up Review Part Correct Of course, neglecting friction, especially air friction, is completely unrealistic at such speeds. Part B A more realistic car would cause the wheels to spin in a manner that would result in the ground pushing it forward with a constant force (in contrast to the constant power in Part A). f such a sports car went from zero to 30.0 mph in time 1.50 s, how long would it take to go from zero to 60.0 mph Express your answer numerically, in seconds. Submit Hints My Answers Give Up Review Part Continue Provide Feedback

Explanation / Answer

Kinetic energy = 1/2 m v2

As speed is double from 30 mph to 60 mph

Energy needed = 22 = 4 times

Time needed reach 60 mph = 4 * 1.5 = 6 s

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v = u + at

final speed is linear to time.

It will take twice time long to reach twice the final speed

So, time to reach 60 mph = 6 s / 2

= 3 secs

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