Force Applied at an Angle to an Object on Frictionless Surface

[jpsmith394]

Homework Statement

The horizontal surface on which the block slides is frictionless. If F = 20 N and M = 5.0 kg, what is the magnitude of the resulting acceleration of the block? The force is applied 30° to the horizontal.

Homework Equations

$F=ma$

The Attempt at a Solution

I began by ignoring the weight and normal force in the vertical axis (y-axis) because the surface is frictionless. Then my next step is to separate the force into compenets with $F_{x}=Fcos\theta$

Therefore:
$ƩF_{x}=Fcos\theta = ma_{x}$

So:
$a_{x}=\frac{Fcos\theta}{m}$

And using the given numbers I got a solution of 3.46$\frac{m}{s^2}$
But the online system I am using shows the correct answer as 7.5$\frac{m}{s^2}$

 

[tiny-tim]

hi jpsmith394! welcome to pf!

erm … you forgot the other F, in front!

 

[jpsmith394]

hi jpsmith394! welcome to pf!

erm … you forgot the other F, in front!

Oh gosh I see now, I was just stuck thinking it was just a single force

Thanks,
James