# An object with mass 5 kg is under constant force (10i+20j)N

1. Nov 20, 2012

### vipson231

An object with mass 5 kg is under constant force (10i+20j)N......

1. The problem statement, all variables and given/known data

(Question is in the attachment)

For the question I used the equation F=ma= m Δ(Vf-vi)/t and plugged in 5 for m and for
velocity I put (vf -(-5+30)/10= (10i + 20j)N. My final equation was

(10i+20j)N= 5(vf-(-5+30)/10

This is as far as I got and I can't solve the question =(. Am i doing something wrong?

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2. Nov 20, 2012

### Mandelbroth

Re: An object with mass 5 kg is under constant force (10i+20j)N......

Vector $\equiv$ fun with a direction. :tongue2:
(10i + 20j) = 5($\vec{v}$$_{f}$-(-5i + 30j))/10

Simplify...
(10i + 20j) = (1/2)($\vec{v}$$_{f}$-(-5i + 30j))

Multiply vectors by the scalar
(10i + 20j) = (0.5)$\vec{v}$$_{f}$-(-$\frac{5}{2}$i + 15j)

Adding the "scaled" initial velocity vector to the other side
(10i + 20j) + (-$\frac{5}{2}$i + 15j) = (0.5)$\vec{v}$$_{f}$

(7.5i + 35j) = (0.5)$\vec{v}$$_{f}$

(15i + 70j) = $\vec{v}$$_{f}$

That's the third answer I see on the attachment, so I might have done this right.

3. Nov 20, 2012

### vipson231

Re: An object with mass 5 kg is under constant force (10i+20j)N......

Thanks a lot man! :D