# Easy question confusing me

#### apples

1. Homework Statement
Two boxes are sitting side on a frictionless surface. The box on the left has a mass of 11kg and the box on the right has a mass of 17kg. If a 90-N force pushes on the 11-kg box from the left, what is the force exerted on the 17-kg by the 11-kg box?

A) 55 N
B) 43 N
C) 68 N
D) 35 N

2. Homework Equations
F=ma

3. The Attempt at a Solution

F=MA
90=(11+17)a
a= 3.2 m/s^2
Since you have to find out the force exerted by the 11-kg box
F=11(3.2)
F=35N

This was a question on a quiz. All my friends got 55N.

Related Introductory Physics Homework Help News on Phys.org

1...3.2m^s^2 is the correct acceleration for both boxes together
2....If you now draw afree body force diagram for both boxes you will see that the 11Kg box has two forces on it the resultant being 90-F where F is the force that the 17 Kg box puts on the 11Kg box
3....There is just one force on the 17Kg box ie F (Newtons 3rd law)
4...In your final step you chose to consider the 11Kg box but you should have wrote
90-F=11a.If you had chosen the 17Kg box you could write F=17a

#### Delphi51

Homework Helper
Oops, I missed that last bit. Yes, 17x3.2 rather than 11x3.2.