Two Horizontal Forces Working On an Object

[richard karn]

Homework Statement

Only two horizontal forces act on a 3.0 kg body that can move over a frictionless floor. One force is 9.0 N, acting due east, and the other is 9.4 N, acting 68° north of west. What is the magnitude of the body's acceleration?

Homework Equations

F=ma

The Attempt at a Solution

Fnet= 9 - 9.4cos(68) = 5.47869

F=ma
5.47869= 3.0 * a
a=1.826232

The right answer is 3.34 though.

 

[PhanthomJay]

Your answer agrees with mine.

 

[cjl]

I disagree. Fnet_x is that, yes, but you forgot about Fnet_y.

(I'm calling East-West the x direction, and North-South the y-direction).

 

[richard karn]

thanks. i was thinking as the other force as pushing into the ground so it wouldn't be accelerating in that direction but then

but 9.4sin(68)/3=2.905

and sqrt(2.905^2+1.8^2) = 3.4

 

[PhanthomJay]

Hmm, the object with a 3 kg mass has a weight force of about 30 N acting down. How can it have acceleration in the y direction?? Then again the problem notes there are only 2 horizontal forces acting, but one of them is neither horizontal nor vertical, it is at an angle. Strangely worded problem. Maybe the object and floor are in a zero g or apparent zero g field? That still doesn't explain the 'horiziotal' force acting 68 degrees north of west.