Did i do this f=ma problem right

[vande060]

1. Homework Statement

A body of mass m = 10 kg initially at rest has force F = 20Ni + 30Nj applied to it. Find its velocity at t = 3 s



f=ma



3. The Attempt at a Solution

m(ai,aj) = (20i,30j

m*ai= 20N

m*aj = 30N

ai = 2*m/s^2

aj = 3*m/s^2

to find the velocities of each of the vectors i used dimensional analysis:

vi = (2*m/s^2) * (3*s) = 6m/s
vj = (3*m/s^2) * (3*s) = 9m/s

to find the complete velocity, i now calculate the magnitude of the vectors by the equation:

v = √( vx^2 + vy^2)

v=√(6^2 + 9^2)


v= 10.9 m/s <--- is that right?

 

[zorro]

yes that is correct.

 

[Redbelly98]

You have the right idea, except that your final answer is not expressed as a vector. They did ask for velocity, and not for the speed.

 

[HallsofIvy]

Yes, velocity is the vector you got initially: [itex]6\vec{i}+ 9\vec{j}[/math] m/s. It is not necessary to find the magnitude- that is the speed.

 

[vande060]

You have the right idea, except that your final answer is not expressed as a vector. They did ask for velocity, and not for the speed.

thanks i never knew the difference between speed and velocity, now i do!