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(8%) Problem 3: Suppose a car approaches a hill and has an initial speed of 118 km/h at the bottom of the hill. The driver takes her foot off of the gas pedal and allows the car to coast up the hill. 33% Part (a) If the car has the initial speed stated at a height of h = 0, how high, in meters, can the car coast up a hill if work done by friction is negligible? 33% Part (b) If, in actuality, a 790-kg car with an initial speed of 118 km/h is observed to coast up a hill and stops at a height 20.5 m above its starting point, how much thermal energy was generated by friction in J? 33% Part (c) What is the magnitude of the average force of friction, in newtons, if the hill has a slope 2.1° above the horizontal? |F_f| =

          (8%) Problem 3: Suppose a car approaches a hill and has an initial speed of 118 km/h at the bottom of the hill. The driver takes her foot off of the gas pedal and allows the car to coast up the hill.
33% Part (a) If the car has the initial speed stated at a height of h = 0, how high, in meters, can the car coast up a hill if work done by friction is negligible?
33% Part (b) If, in actuality, a 790-kg car with an initial speed of 118 km/h is observed to coast up a hill and stops at a height 20.5 m above its starting point, how much thermal energy was generated by friction in J?
33% Part (c) What is the magnitude of the average force of friction, in newtons, if the hill has a slope 2.1° above the horizontal?
|F_f| =

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(8%) Problem 3: Suppose a car approaches a hill and has an initial speed of 118 km/h at the bottom of the hill. The driver takes her foot off of the gas pedal and allows the car to coast up the hill.
33% Part (a) If the car has the initial speed stated at a height of h = 0, how high, in meters, can the car coast up a hill if work done by friction is negligible?
33% Part (b) If, in actuality, a 790-kg car with an initial speed of 118 km/h is observed to coast up a hill and stops at a height 20.5 m above its starting point, how much thermal energy was generated by friction in J?
33% Part (c) What is the magnitude of the average force of friction, in newtons, if the hill has a slope 2.1° above the horizontal?
|Ff| =

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University Physics with Modern Physics

Hugh D. Young 14th Edition

Instant Answer

Solved by Expert Ivan Kochetkov

03/25/2022

Step 1

The kinetic energy is given by (1/2)mv^2, where m is the mass of the car and v is its speed. The potential energy at the top of the hill is mgh, where g is the acceleration due to gravity and h is the height of the hill. Setting these two equal to each other, we Show more…

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Problem 3: Suppose a car approaches a hill and has an initial speed of 118 km/h at the bottom of the hill. The driver takes her foot off of the gas pedal and allows the car to coast up the hill. Part (a) If the car has the initial speed stated at a height of h = 0, how high, in meters, can the car coast up a hill if work done by friction is negligible? Part (b) If, in actuality, a 790-kg car with an initial speed of 118 km/h is observed to coast up a hill and stops at a height 20.5 m above its starting point, how much thermal energy was generated by friction in J? Part (c) What is the magnitude of the average force of friction, in newtons, if the hill has a slope 2.1° above the horizontal?

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Transcript

00:01 Hi there, here we have to solve an assignment of three questions and i already solve two.

00:05 I'm going to walk you through the solution and then solve the remaining one.

00:08 First of all, we have to convert speed from kilometers per hour to meters per second and to do so we divide the speed by 3 .6.

00:16 And that is the speed in meters per second.

00:20 Now in question a we have to calculate maximum height which can be achieved if there is no friction and this height can can be calculated from the conservation of mechanical energy.

00:34 Maximum height equals to squared velocity square speed divided by 2g, which is 54 .8 meters.

00:41 In question b, there is a friction and we have to calculate the heat release due to this friction.

00:47 So initial kinetic energy is now converges into potential energy at the end, plus the amount of dissipated heat.

00:55 And this amount of the dissipated heat equals to 267 kilojoules.

01:00 So now we have to solve question problem c where we have to define the magnitude of the average force of friction in newton's if the heel has a slope of 2 .1 degree above the horizontal.

01:16 Let's illustrate it.

01:25 Here we have to find the average force.

01:28 So that is the slope, alpha.

01:32 This is the height, the shift in question b.

01:36 That is 20 .3 meters...

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