(a) How high a hill can a car coast up (engine disengaged) if friction is neglig

Question

(a) How high a hill can a car coast up (engine disengaged) if friction is negligible and its initial speed is 90.0 km/h? Incorrect: Your answer is incorrect. m (b) If, in actuality, a 750 kg car with an initial speed of 90.0 km/h is observed to coast up a hill to a height 14.0 m above its starting point, how much thermal energy was generated by friction? J (c) What is the average force of friction if the hill has a slope 2.5° above the horizontal? (Explicitly show on paper how you follow the steps in the Problem-Solving Strategy for energy found on pages 159 and 160. Your instructor may ask you to turn in this work.) N (down the slope)

Explanation / Answer

v= 90.0 km/h = 25m/s

a) KEi = PEf

1/2mv^2= mgh

h=v^2/2g = (25^2)/(2*9.8) = 31.9 m

b) WThermal = KEi – PEf = 1/2mv^2 – mgh = ½*750*25^2 - 750*9.8*14 = 131475 J

c) WThermal = Ff*d = Ff *(h/sin2.5)

131475 = Ff*(14/sin2.5)    => Ff = 409.6 N

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