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Question about velocity

  1. Jan 8, 2015 #1
    I was thinking of an object let's say object A has a maximum velocity of 50mph and weighs 100lbs if I added another 100lbs what would be the maximum velocity of the object A? I also want to know what topic is this concern for me to study and enable myself to answer this types of question.

    So I was thinkg KE = 1/2(mv^2)

    Last edited by a moderator: Jan 9, 2015
  2. jcsd
  3. Jan 8, 2015 #2
    Velocity isn't determined by mass, so the question isn't really sensible. The only limit on the velocity is the speed of light. It takes a force to increase the velocity of an object, and the faster you want to go and the heavier an object is the more force you need to get to that point. So doubling the mass would simply mean you'd need more Force to accelerate the object to get to 50 mph. This is the whole idea behind Newton's Second Law.
  4. Jan 10, 2015 #3


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    Hi, BeefSteak, I hope you did not let yourself frighten away . Welcome to PF! This is a good place, if you stick to the rules. You are offered a template when you start a thread, and you must not delete it.
    I wonder what your question really is. What do you mean on maximum velocity? Please, copy the whole problem text.
  5. Jan 10, 2015 #4
    A (wheeled) vehicle has two drag forces limiting its top speed.
    (level ground assumed)
    1) air drag force, which increases (exponentially) with velocity.
    2) rolling resistance drag force which is deemed to be constant regardless of velocity, and depends on :
    mass (m) in kg
    local gravity rate (g) (9.81 m/s/s is usual)
    tyre to road rolling resistance co-efficient (Crr) (0.03 is a good figure)
    Assuming all the tyres are the same, the rolling resistance drag force (f) in Newtons you get from :
    f = m * g * Crr
  6. Jan 10, 2015 #5


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    Staff: Mentor

    An exponential increase would be very unusual, for typical vehicles and the given speed a quadratic dependence is a much better approximation.

    Without more details of the vehicle, we cannot tell which influence is more important, and we also don't know what limited the speed before. It is unlikely (but not impossible) that the vehicle will be able to become faster, it is unlikely that its top speed will go down below half of the original value, but everything in between is possible.
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