Car mass is 1500kg, starts from rest and accelerates to 18m/s in 12.0 seconds. Assume the air resistance remains constant at 400.0N during the time, what is the average power developed by the engine?
2007-12-11 19:20:40 · 2 answers · asked by Anonymous in Science & Mathematics ➔ Physics
Power = Energy transferred / time taken
Energy transferred = Gain in K.E + work done against friction
Gain in K.E = 1/2 x mass x (velocity)²= 1/2 x (1500) x (18)² =243000 J
Work done against friction = Force x distance moved in direction of force
Force= 400
Distance = ??
Lets calculate the distance
but first lets calculate the acceleration
v=u+at
18=(0)+a(12)
a=1.5m/s²
V²=2as+U²
(18)²=2(1.5)(s)+(0)²
s=108 m
Work done against friction = Force x distance moved in direction of force
Work done = 400 x 108 = 43200 J
Power = Energy transferred / time taken
Energy transferred = 243000 + 43200 =286200 J
Time taken = 12 s
Power = 286200 / 12
Power= 23850 Watt
2007-12-11 19:31:46 · answer #1 · answered by Murtaza 6 · 0⤊ 0⤋
The total energy applied is the final kinetic energy plus the frictional energy.
KE = 0.5*m*v^2
FE = Fr*s, where s is the distance traveled.
The distance traveled is s = 0.5*a^t^2; a = 18/12 = 1.5 m/sec^2, so s = 108 m
KE = 243000 J
FE = 400*108 = 43200 J
Total E = 286200 J
This is expended in 12 s, so the power is 23850 W
2007-12-12 03:37:30 · answer #2 · answered by gp4rts 7 · 0⤊ 0⤋