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Homework Help: How to calculate time when given distance, mass, and power

  1. Dec 1, 2015 #1
    1. The problem statement, all variables and given/known data
    I need to calculate the time that it takes for a drag car that is powered by an 8 gram CO₂ cartridge to go across a certain distance. My wooden drag car is 100 grams. It will be traveling a distance of 50 feet.

    2. Relevant equations
    Force= mass x acceleration
    Power= work / time
    Work= force x distance
    Time= distance / speed
    Power= force x velocity

    1 gram = 0.001 kilograms
    1 ft = 0.33 meters

    3. The attempt at a solution
    I've tried to find out how much power is produced by the CO2 cartridge. I could not find an answer, which made me think that maybe I dont need to find power. Also, power is measured in watts and no where in my statement do I mention watts. I do not know the speed of my car yet. How do I calculate the time?
  2. jcsd
  3. Dec 2, 2015 #2
    This depends on things you have not accounted for here. There's friction, not just with the surface, but in the axles. Also, you need to know how much power is exerted by a cartridge. It's not exerted all at once, and it's not constant, and it quickly putters out.
    Also, is your car guided by a wire, or is it possible for it to deviate from a straight path?
  4. Dec 10, 2015 #3

    Buzz Bloom

    User Avatar
    Gold Member

    Hi Sky:

    I think that since the problem statement does not mention friction, you can assume it is negligible. I also think it is reasonable to assume the car will go in a straight line.

    I do not know how much energy there is in a 8 gram CO2 cartridge. Have you tried to find this out, as well as other specs, by searching the Internet? I tried too find out how much CO2 is in an 8 gm cartridge, but failed to find this, or about pressure or any other specification. In the absence of this information, you might make some assumptions to see what assumptions produce what answers. It seems like a strange homework problem requiring many hypothetical assumptions, not all of which need to be realistic.

    Assume 8 grams of CO2. Assume some mass for the container holding the CO2 at some pressure. Assume the CO2 would be released at a constant rate and empty in t seconds. Make assumptions about the velocity in which the gas exits the nozzle. I am guessing the problem wants you take into account that the mass of the car together with the cartridge reduces as cartridge empties.

    Good luck.

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