Find Force F2 Given F1 & a - Homework Statement

[Amel]

Homework Statement

Two forces F1 and F2 are acting on a mass M=4kg. The force F1 = 11i + 5j + 7k, in N. The acceleration of the mass is given by a = 3i + 7j + 4k, in m/s². Calculate the magnitude of F2 .

Homework Equations

F = ma

The Attempt at a Solution

Ok so what I tried here is doing F1 + F2 = ma
so F2 = (ma)- F1

I took a = 3i + 7j + 4k and multiplied all of the components by 4kg got 44i+20j+28k and then subtracted F1 = 11i + 5j + 7k and got 41i+13j+24k kg*m/s^2

what do I do?

 

[rock.freak667]

I took a = 3i + 7j + 4k and multiplied all of the components by 4kg got 44i+20j+28k and then subtracted F1 = 11i + 5j + 7k and got 41i+13j+24k kg*m/s^2

what do I do?

ma=4(3i+7j+4k)=12i+28j+16k


now subtract this from F1

 

[Amel]

so i+23j+3k ? what units do I use for this? its saying I am not using the right units. Isn't it N*m/s^2

 

[rock.freak667]

so i+23j+3k ? what units do I use for this? its saying I am not using the right units. Isn't it N*m/s^2

'ma' is in N

F₁ is in N


so if F₂= ma - F₁, then F₂ is in N as well.

 

[Amel]

cool I got it right it was 1i+23j+9k square the coeficents add them up and then square root to find the force N.