(a) How high a hill can a car coast up (engine disengaged) if friction is neglig
ID: 1394860 • Letter: #
Question
(a) How high a hill can a car coast up (engine disengaged) if friction is negligible and its initial speed is 80.0 km/h? m (b) If, in actuality, a 750 kg car with an initial speed of 80.0 km/h is observed to coast up a hill to a height 11.0 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 degree 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
a)
initial speed , u = 80 km/h
u = 22.2 m/s
if there is no friction , using conservation of energy ,
0.5 * m*v^2 = m*g*h
0.5 * 22.2^2 = 9.8 * h
h = 25.2 m
the height car climb is 25.2 m
b)
let the internal energy generated by friction is Wf
Wf + m*g*h = 0.5 mv^2
Wf + 750 * 9.8 * 11 = 0.5 * 750 * 22.2^2
Wf = 104335 J
the thermal energy generted is 104335 J
c)
let the friction force is f ,
Wf = f*d
104335 = f * 11/(sin(2.5))
f = 413.7 N
the frictional force is 413.7 N
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