Finding acceleration of box- given mass of box and magnitude of frict

[13physicsdude]

Finding acceleration of box-- given mass of box and magnitude of frict

Doing homework and stuck on this question. A student pushes a 10kg box and let's it slide across the floor. The magnitude of the frictional force acting on the box is 40 N. What is the acceleration of the box?


Relative equations:
Fnet=ma
a=fnet/m

Attempt:

Fnet=ma
a=fnet/m
a=40N/10kg
a=4 m/s2

I know this is probably wrong, I am just so confused...

 

[Simon Bridge]

acceleration is a vector ... you need to include the direction somehow.
Apart from that you are quite correct - there is only one force on the box and F=ma.