Really simple Force question! (1 Viewer)

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

A 2-kg block A and a 3-kg block B are in contact on a frictionless table. A horizontal force of 10N is applied to A. Find the force with which B resists the pressure of A.

The answer is -6N. I realize this is a very simple question, I would just like to understand how to get the solution. Thanks in advance :)


Homework Helper
Hi aishax, welcome to PF.

Start with drawing some free-body diagrams:
- One of the complete system (A + B)
- One of A only
- One of B only
Hint: The force felt by B must be the amount that makes it accelerate at the same rate as A and as A+B.

What are the "external forces" in each case?
Hello mezarashi :)

Alright, I drew each of those FBDs. I found the acceleration of the system, which was 2.0 m/s^2. I used the acceleration, and found the Fapp on mass A, which was 4.0 N. And Fapp for mass B is 6.0 N.

The external forces are Force normal, and force applied. I'm still a tad lost on the concept still, unfortunately.
Last edited:

The Physics Forums Way

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving