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A couple of definitions before doing this problem:

Watts is the measure of power to do something

Power (P)=Work(W)/Time(t)

W=Force(F)*distance (d) *cos(Angle) (for this problem I’m going to assume that the force is in the direction of travel)

F=Mass (m) *acceleration (a, or dv/dt)

this is two part problem, do the total Power would be the sum of the Power for each part

Part 1

m=150kg

t=10s

a=100/10=10m/s/s

d=(1/2)*10m/s/s*(10s)^2=500m

F=150kg*10m/s/s=1500N

W=1500N*500m=750000J

P=750000J/10s=75000W

Part 2

m=150kg

t=10s

a=(140-100)/10=4m/s/s

d=(1/2)*4m/s/s*(10s)^2=200m

F=150kg*4m/s/s=600N

W=600N*200m=120000J

P=120000J/10s=12000W

Total P=12000W+75000W=**87000W**

Is somewhat off, part 1 = is 0-100 KM/h so 50 km/h avg.

50km/h / 3600s = 13.88 m / s Avg speed first 10 seconds.

13.88m/s * 10s = 138.8 meters.

F=150kg*10.00m/s/s*=1500N

W=1500N*138.8m=208200J

P=208200J/10s=20820W

P = 2,082 KW

Next part is not 120km/h - 100km/h, it is 140+100/2 = 120km/h

120km/h / 3.6 = 33.333 m/s avg. through the last 10 seconds...

and thus travels 333 meters.

F=150kg*4m/s/s=600N

W=600N*333M = 199800J

199800J/10s = 19980W

= 1,99 Kw

1,99 Kw + 2,082 Kw = 4,072 Kw

not sure this is right, my computer uses 0.4 Kw... 10 of my computers could move a 150kg object that fast?....

I took the formula Vindurnott, though. Just fixed the distances...

There is a better way of calculating the straight forward kinetic energy=0.5 MV^2 that on average is beeing measured....

0.5 * 150kg * ( 120+50/2 ) ^2 = 1576875 Joule

1576875/20s = 78843,75 Watt

= 78,84375 kilowatt for constant 85 km/h travel.

[/FONT] but by calculating energy=0.5*150*(140km/h)^2 = 1470000 joule to go 140km/h

energy=0.5*150*(100km/h)^2 = 750000 Joile to go 100 km/h

1470000/750000 = 1,96 ratio. It nearly doubles the amount of energy needed from 100 to 140.

while the amount of energy for the average speed ( 120 ) = 75*(120)^2 = 1080000 joule.. 1080000/750000 = 1.44

100km/h = 100

120km/h = 1.44

140km/h = 1,96 thus the maximum needs to be 1,88 for average value to work, but its not. it is 0.08 higher

so instead of 1080000 Joule it is actually 1080000*(1+0.04) = 1123200 Joule ( note that the increase is halved, because it is an average of the 2 diferrences.. )

Doing the same thing with the 0-100 section of acceleration,

0 = 0

50 = 75*(50^2) = 187500 J

100 = 75*(100^2) = 187500 = 750000J

0 = 0

187500J = 1

750000 = 4,016.

187500 * (4,016/0.50) = 376500 Joule.

1080000*(1+0.04) = 1123200 Joule

376500 + 1123200 Joule = 1499700 Joule

1499700/20 = 74975 Watt

= 74,975 Kilowatt

Hmm...im not going to go closer than this, without drawing a graph..... but this is what i worked out

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