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# M2 help (edexcel) watch

1. 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!
2. (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).
3. (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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