- #1

cassie123

- 15

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## Homework Statement

Three boxes are in contact with each other on a frictionless horizontal surface as shown. The masses of the boxes are m1 = 10 kg, m2 = 20 kg, and m3 = 30 kg. A horizontal force F = 90 N is applied to m1.

Calculate:

a. the acceleration of the three boxes.

b. the net force on each box.

c. the contact forces between the boxes.

## Homework Equations

Newtons second law

F=ma

## The Attempt at a Solution

total mass = 60 kg

F = ma

1) a = F/m = 90/60 = 1.5 m/s^2

2) net force on each box

F1 = m1a = 10*1.5 = 15N

F2 = m2a = 20*1.5 = 30 N

F3 = m3*a = 30 *1.5 = 45 N

Am I missing forces in calculating the net force?

c) contact force

90-15 = 75 N btwn 1st and 2nd box

75- 30 = 45 N btwn 2nd and 3rd box

The above is my best guess although I am not confident that this is the way to calculate contact forces. (What are contact forces?) Should I be using something like f=(F*(m2+3))/(m1+(m2+3) or f=(F*m2)/(m1+m2) to find the contact force between boxes 1 and 2?