# M1 help!

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#1
Hola, basically I'm doing M1 and I kind of hate maths at the moment so bare with me if I ask any ridiculous really obvious questions.

I've got an old exam question from 2003 & our teacher gave us all the final answer for it but I'm confused as to how she got it.

5. A particle P moved with constant acceleration (2i-3j)m/s^-2. At time t seconds, it's velocity is v/m/s^-1. When t=0, v=-2i+7j.

a. Find the value of t when P is moving parallel to the vector i. (I've done this bit & got it correct. The answer is t= 2 and a third seconds.)

b. Find the speed of P when t=3. (this is the bit I'm ridiculously stuck on. I don't understand how to get to the answer, is there a formula or something I should know about that and I'm just being a bit dense?)

c. Find the angle between the vector j and the direction of motion of P when t=3. (Haven't yet tried this, but I suck at maths so all help would be appreciated.)

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6 years ago
#2
(Original post by tamsinaribena)
Hola, basically I'm doing M1 and I kind of hate maths at the moment so bare with me if I ask any ridiculous really obvious questions.

I've got an old exam question from 2003 & our teacher gave us all the final answer for it but I'm confused as to how she got it.

5. A particle P moved with constant acceleration (2i-3j)m/s^-2. At time t seconds, it's velocity is v/m/s^-1. When t=0, v=-2i+7j.

a. Find the value of t when P is moving parallel to the vector i. (I've done this bit & got it correct. The answer is t= 2 and a third seconds.)

b. Find the speed of P when t=3. (this is the bit I'm ridiculously stuck on. I don't understand how to get to the answer, is there a formula or something I should know about that and I'm just being a bit dense?)

c. Find the angle between the vector j and the direction of motion of P when t=3. (Haven't yet tried this, but I suck at maths so all help would be appreciated.)

The velocity vector in time of t, is sum of two components vectors.
1. THe velocity in t=0 which is -2i+7j and remain constant
2. The velocity from acceleration which is parallel with the vector
of acceleration and the value of this after t time is t*a ->2ti-3tj
Adding together, the velocity vector at the time of t
v=(2t-2)i+(7-3t)j
For t=3 sub in t 3
For the magnitude of the velocity
|v|=V(2t-2)^2+(7-3t)^2

For angle between j (y direction) and the vector consider that
vy/v=cos (alpha)
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#3
(Original post by ztibor)
The velocity vector in time of t, is sum of two components vectors.
1. THe velocity in t=0 which is -2i+7j and remain constant
2. The velocity from acceleration which is parallel with the vector
of acceleration and the value of this after t time is t*a ->2ti-3tj
Adding together, the velocity vector at the time of t
v=(2t-2)i+(7-3t)j
For t=3 sub in t 3
For the magnitude of the velocity
|v|=V(2t-2)^2+(7-3t)^2

For angle between j (y direction) and the vector consider that
vy/v=cos (alpha)
Thank you so much! You really helped & now I've finally got all my hw done, thanks again.
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