Question

Problem 2 A force F 25N pushes three boxes with masses m m3 8kg as shown in Figure 4.38 5kg, m2 2kg and Figure 4.38: Problem 2 G) What is the acceleration of the system? (ii) What is the contact force between box 1 and box 2? (iii) What is the contact force between box 2 and box 3?

Answer 1

1) Considering system of three masses. Net external force on the system is
F = 25 N
Mass of system = 5+2+8 = 15 kg
Accelerattion of system = net external force / mass
                                      = 25/15 = 1.7 m/sec²

2) Considering system of masses 2 and 3. Net external force on this sytem is contact force from mass 1 on mass 2. Let this contact force be N1.
Total mass of this system = 2 +8 = 10 kg
Acceleration of this system = 1.7 m/sec²
N1 = m*a = 10*1.7 = 16.7 m/sec²

3) similarly for system of mass m3, external force is contact force N2, exerted by m2.
N2 = m3 * a
     = 8*1.7 = 13.3 m/sec²