look at forces, work and energy of motor vehicles. Consider a 900-kg car coastin
ID: 1964449 • Letter: L
Question
look at forces, work and energy of motor vehicles.Consider a 900-kg car coasting down an inclined road at a constant velocity of 110km/h. The grade of the road is 15%, which means tan A = 0.15, where A is the angle of incline.
Draw a free body diagram of the car on the incline and determine the drag force on the car. We know the drag force on the car when it is traveling at 110km/h.
What is the kinetic energy of the car when it is moving at 110km/h? Use this kinetic energy to find the work required to accelerate the car to this speed from rest.
Use the drag force you found above to calculate the work done on the car by drag over 110-km (watch units!). To keep the car moving at 110km/h the car's engine supplies "energy" to the car. The rate it supplies energy is called Power and is the energy divide by time. since it takes 1 hr to go 110km, calculate the power of the engine in Watts=J/s (watch units). Convert this to horsepower.
Finally, given the energy density of gasoline is 34MJ/litre, how many litres of gas are used in this 110km trip? Does that seem reasonable?
Explanation / Answer
car is moving down at constant velocity. so drag force= m*g*sin()
tan()= .15
or,= 8.530
drag force= 900*9.81*sin(8.53)
=1309.58 N
kinetic energy= .5*900*v^2
v=110*1000/3600= 30.56 m/sec
kinetic energy= 420.26 KJ
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