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    A particle P of mass 0.2 kg is at rest at a fixed origin O. At time t seconds, where 0 ≤ t ≤ 3 , is a force (2ti + 3j)N applied to P.

    a) Find the position vector of P when t = 3.
    r = 45i +67.5j (I worked it out with no problem)

    b) When t = 3, the force acting on P changes to (6i + (12 - t^2)j)N, where t ≥ 3. Find the velocity of P when t = 6.

    I got as far as v = 30ti + (60t - 5/3 t^3)j +c (by using F=ma to find acceleration then integrating it to find velocity)
    I don't know how to work out C.
    Help is appreciated!
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    (Original post by ManLike007)
    A particle P of mass 0.2 kg is at rest at a fixed origin O. At time t seconds, where 0 ≤ t ≤ 3 , is a force (2ti + 3j)N applied to P.

    a) Find the position vector of P when t = 3.
    r = 45i +67.5j (I worked it out with no problem)

    b) When t = 3, the force acting on P changes to (6i + (12 - t^2)j)N, where t ≥ 3. Find the velocity of P when t = 6.

    I got as far as v = 30ti + (60t - 5/3 t^3)j+ c (by using F=ma to find acceleration then integrating it to find velocity)
    I don't know how to work out C.
    Help is appreciated!
    From a) you can work out the velocity when t = 3.

    Use that as your initial conditions for part b).
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    (Original post by notnek)
    From a) you can work out the velocity when t = 3.

    Use that as your initial conditions for part b).
    Ahh I see, thanks for your help!
 
 
 
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