7.4 | Suppose a car travels 108 km at a speed of 30.0 m/s, and uses 2.0 gal of gasoline. Only 30% of

Suppose a car travels 108 km at a speed of 30.0 m/s, and uses 2.0 gal of gasoline. Only 30% of the gasoline goes into useful work by the force that keeps the car moving at constant speed despite friction. (See Table 7.1 for the energy content of gasoline.) (a) What is the magnitude of the force exerted to keep the car moving at constant speed? (b) If the required force is directly proportional to speed, how many gallons will be used to drive 108 km at a speed of 28.0 m/s?

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[GlaserTutoring]

Hi everyone - the answer for part (a) should be 6.7 x 10^2 N. I must have forgotten to plug the number 2 into the calculator when I calculated the energy. Whoops 🙃

[mandoloon]

I have to comment and thank you, I would be failing this class and losing my financial aid if it wasn't for your videos! Your Ray Ramano-like voice and your sense of humor have made this course enjoyable. I read these problems alone and can't comprehend a thing, but when you read them and explain it visually it just all makes sense! Thank you so so so much.

[johnsansone]

8:23 "Quite honestly, who cares about significant figures anymore" 🤣 I'm happy someone else is saying it!

[krystyhawk]

Thank you for keeping these videos up. Being able to compare processes helps me to learn rather than being stuck. I do not have direct access to teachers or tutors right now. I am glad resources like this exist.

[sarahedwards]

Shouldn't the answer for part a be 667N instead of 333N? It appears as if the calculation for the work done by the gasoline didn't include 2 gallons of gas even though it was written down.

[abrahamvillegas]

you are the best teacher! you got my sub!

[TheTragicOof]

thank you not only did I end up doing the problem correctly but you also gave me insight for future problems!

[samishubert]

my answer for part A was 794. I used the numbers 108, 000km, 25 m/s, 30% gas useful, 2.2 gallons of gas, 1.3 x 10^8 J per gallon.

[wiadomokto]

In the question they say "force is directly proportional to speed" not to the volume of gasoline. Although the answer for (b) is correct (all the quantities present here are directly proportional) but it's not that straitforward and worth mentioning in the solution, at least in my opinion.

[ianproctor]

I keep getting 7.2x10^7 for the amount of joules in part a instead of 3.6x10^7