Three blocks move on a surface with μs = 0.6 and μk = 0.4 as shown below. Jennifer, another
honor chemistry student, applied 34 N of force to move the system of three blocks, but she
failed. Assume that the string is massless.
(a) Michael asked why. Can you answer to Michael?
(b) Now, the determined Jennifer applied 50 N of force to the system. Draw free‐body diagrams
for each of blocks.
(c) Write down the equations of motions for all three blocks. What are net forces?
(d) Find the acceleration.
(e) Find the tension and the contact force between the first and second block.
(a) 34 N force is not enough to overcome the force of friction = 0.6 ( 1*g +2*g +3*g) = 35.28 N
(b)When force is 50N , Force of friction = 0.4(6 *g) = 23.52 N ( Static coefficient is replace by kinetic)
Net force on three blocks = 50 N - 23.52 N = 26.48 N
Acceleration of all the blocks together = Force / Mass = 28.48 /6 = 4.41m/s2
Tension in the string connecting two sets of blocks = T = 3*4.41 + 0.4*3*9.8 = 13.23 +11.76 = 25.0 N
This is tension on 3 kg block as well on 2kg block
