# Newton's Second law: Pushing the box

1. Homework Statement

How much force is needed to push a 20 kg box across a floor at a constant speed of 0.5 m/s [forward] against a frictional resistance of 4 N?

Fnet = m.a

## The Attempt at a Solution

Since the velocity is constant, the acceleration will be 0. If that is correct the net force is going to be 0, which doesnt make any sense.

## Answers and Replies

gneill
Mentor
Since the velocity is constant, the acceleration will be 0. If that is correct the net force is going to be 0, which doesnt make any sense.
Why's that? Did you draw the Free Body Diagram?

cnh1995
Homework Helper
Gold Member
If that is correct the net force is going to be 0, which doesnt make any sense.
The "net" force is zero. You are asked to find the force that needs to be "applied" to the box.

Chestermiller
The "net" force is zero. You are asked to find the force that needs to be "applied" to the box.
Is there a formula that I can use to find the "applied force"?

gneill
Mentor
Is there a formula that I can use to find the "applied force"?
That's the purpose of this exercise: You're meant to find that formula by analyzing the problem using the given information.

As already mentioned, you need to draw the FBD to see how the forces combine.

cnh1995
That's the purpose of this exercise: You're meant to find that formula by analyzing the problem using the given information.

As already mentioned, you need to draw the FBD to see how the forces combine.
Is it going to be 4N because the forces have to be balanced?

cnh1995
Homework Helper
Gold Member
Is it going to be 4N because the forces have to be balanced?
Yes.

aatari