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## Solution for problem 65PE Chapter 7

College Physics | 1st Edition

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Problem 65PE

Problem 65PE

Unreasonable Results

A car advertisement claims that its 900-kg car accelerated from rest to 30.0 m/s and drove 100 km, gaining 3.00 km in altitude, on 1.0 gal of gasoline. The average force of friction including air resistance was 700 N. Assume all values are known to three significant figures. (a) Calculate the car’s efficiency. (b) What is unreasonable about the result? (c) Which premise is unreasonable, or which premises are inconsistent?

Step-by-Step Solution:

Part (a)

Step 1 of 6:

The speed of the car is provided. The car has gone to 100 km distance and gained 3.00 km altitude. The car must possess the kinetic and potential energy if it moves at a height. The motion of the car is affected by external resistances like friction and air resistance. We are going to find the efficiency of the car.

The mass of the car The final speed of the car  The initial speed of the car The height gained by the car or The distance traveled or The frictional force The acceleration due to gravity Step 2 of 6:

The efficiency of the car is the ratio of the work output and the total energy input.

The Efficiency of the car The total energy input of 1gal of gasoline is given as Step 3 of 6:

The work output of the car is the sum of the kinetic energy, potential energy and the work done by the frictional forces. Substituting the known values  Step 4 of 6

Step 5 of 6

##### ISBN: 9781938168000

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