# Vector Forces

## Homework Statement

Three forces, given by 1 = ( -2.35 i - 2.10 j ) N, 2 = ( 4.90 i + 3.05 j ) N, and 3 = (49.0 j ) N, act on an object to give it an acceleration of magnitude 3.65 m/s2.

(a) What is the direction of the acceleration?
86.1° (from the positive x axis)

(b) What is the mass of the object?
_____kg

(c) If the object is initially at rest, what is its speed after 10.0 s?
_____m/s

(d) What are the velocity components of the object after 10.0 s?
(____ i + ____ j) m/s

F = ma
Vf = Vi + at

## The Attempt at a Solution

F = ma
m = F/a
To find mass (kg), I divided 2.55 by 3.65 and got 0.7 kg as the answer. That should be the correct answer but it isn't. Can someone please tell me what I did wrong? Thanks.

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mjsd
Homework Helper
where did you get 2.55 for magnitude of force?

2.55i + 49.9j were the magnitudes.

I found I was supposed to use 49.9 as the F, and that resulted in a mass of 3.68 kg, which is the correct answer.

Now I just need to solve for the i component for part d.). I got 36.42j for the j component, which is right, and 2.48i as the i component, which is wrong.
Help?

mjsd
Homework Helper
the magnitude of this vectorial quantity (2.55, 49.95) is given by

$$\sqrt{2.55^2 + 49.95^2} \approx 50$$ and NOT 49.9, although in this case it turned out that it is close to 49.9

Ok that is right.

However I wasn't able to find the i factor of velocity components after 10 second

For part d

Last edited:
mjsd
Homework Helper
did you mean to say mass is about m= 13.7 Kg?
then 2.55/m x 10 = 1.86
49.95/m x 10 = 36.4