When an automobile moves with constant velocity, the power developed is used to overcome the frictional forces exerted by the air and the road. If the engine develops 30 hp, what total frictional force acts on the car at 120 mph?
1hp = 746W
1mile-1609m
work=force*distance
power= work/time
30hp= 22380w
120mph= 53.6448m/s
I'm really not sure where to go from there, you need to end up with force which is Newtons, dont you need a mass in kg to for that?
2007-11-26 15:30:32 · 2 answers · asked by Katie E 2 in Science & Mathematics ➔ Physics
You have all of the pieces already. Consider the motion of the car for one second.
The work done in one second is 22,380 J.
Since this work is done to overcome the net friction force, it must be equal to the friction force * distance, so take the distance covered in 1 second at 120 mph (53.6 meters) and solve for the force.
22,380 J = F ( 53.6 m )
F = 22,380 J / 53.6 m
2007-11-26 16:16:00 · answer #1 · answered by jgoulden 7 · 0⤊ 0⤋
A watt is a joule per second. So the car is using 22380 joules every second. How far does the car travel in a second? 53.6448 m. So the car is using 22380 joules for every 53.6448m.
22380joules per 53.6448m = 22380j/53.6448m
a joule is a kg m^2/s^2
do the division and your answer will be in newtons
2007-11-27 00:16:32 · answer #2 · answered by Aaron777 3 · 0⤊ 0⤋