I just need my work checked here. Please let me know if I am correct. I had this problem in one of my test in which I did not get full credits. I am re-doing this(hopefully correctly this time) just for my own peace of mind and understanding.
Problem statement: The force shown of 6.4N pulls horizontally on the 1.5kg block that is connected by a string to the second block of mass 0.93 kg. Assuming a smooth friction less surface find acceleration of the blocks and tension in the string. If there is friction, what happens to the tension in the string? (increase, decrease, stay the same? show your logic)
The system and my free body diagram:
Given: m1 = 1.5 kg
m2 = .93 kg
F = 6.4 N
Total Mass = m1+m2 = 2.43 kg
F = ma
F = (m1 + m2)a
6.4N = (2.43kg)a
a = 2.63 m/s2
m1 = (1.5 kg)(9.81m/s2)= 14.7 N
m2 = (0.93 kg)(9.81m/s2)= 9.11 N
T = (m1+m2) + 6.4 N = 14.7 N + 9.11 N + 6.4 N = 30.4 N
If there is friction, the tension would increase. As the friction increases the force that pulls the two objects would have to be greater therefore increasing the tension.(The way I thought about is if there was friction, the blocks would require more force to move, since we already established that the net force is 6.4, the tension would have to increase to balance the frictional force.)
I just wanted to make sure that I at least had the correct concept down. Any, criticism and suggestions are welcome.