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Saturday, May 27, 2006

a loophole in lion hunting

Hey LION HUNTER!!

Ur ideas to catch a lion were gr8! But one of the methods, which involved that we run in same direction as lion, so that he runs faster from our frame of reference and gets tired soon is not a matter of joking at, there’s something serious in it.

There’s a related question:

Assume a small car with engine pulls at constant force F and the car moves with a constant velocity V. Power generated P=FV. But a cyclist riding at constant speed U observes power P=F(V-U). Petrol consumption is directly proportional to the power generated. Then the question is:

WHY THE RATE OF PETROL CONSUMPTION SAME FROM BOTH FRAMES WHEREAS POWER GENERATED BY THE ENGINE DIFFERENT?

7 comments:

TwIsTeR said...

Heyy
a certain loophole in this question...
Is a constant force is applied, how can the care move with a constant velocity ? The question is not clear from this point of view, cud u elaborate plz ....

~ Twish ~

saurya_time_travel said...

nice one prav ... but i think only one line can answer ur question very well ...(i didnt understand ur question well) ... the philosophy of relativity is that "truth is relative" ... mark my words. The rate of petrol consuption can (i cant say it will) be different for different observers ...
plz elaborate on the power formula u gave ...

time travel

Pravar D Mahajan said...
This comment has been removed by a blog administrator.
Pravar D Mahajan said...

u need the formula of power

power=dw/dt=F(dx/dt)=FV

V=velocity

Pravar D Mahajan said...

the constant force is the applied to overcome the frictional force between tyres and the road. hence the net force on the car is zero

Lagnajeet_Das said...

hey prav

Ur questions is correct. The answer is

When u r measuring the power consumption of the car wrt to the cycle u r actually measuring the extra amt of power generated by the car wrt to the cycle.
i.e. u r subtracting the power of the cycle from the total power of the car . So u get a relative power not the absolute power.
so the petrol consumption seems to have decreased which actually doesn't happen so.

Lagnajeet
Lion Hunter

RG said...

Relativity is complex in that you have to consider both the frame of observation and the observed frame.

Over here, the rate of consummation of fuel (total) is equal to the energy evolved. You forget the biological energy used by the bicyclist to keep up with the car. For him, the car does not move so fast, but the force remains the same; the concept of power in the two cases is incomparable.