The two blocks in the figure(Figure 1) are sliding down the incline.What is the tension in the massless string?
Concepts and reason
The concepts required to solve the given problem are Newton’s second law of motion and tension.
First, determine the acceleration of the blocks by finding the net force acting on each block. Then, determine the tension in the string by using the net force acting on one of the block.
Fundamentals
Newton’s second law of motion states that the net force acting on an object is directly proportional to the product of its mass and acceleration.
According to Newton’s second law, net force acting on an object is,
F = ma
Here, m is the mass of the object and a is the acceleration of the object.
Tension is a pulling force transmitted through a string, cord or wire. Tension is directed along the length of the wire and it is due to the forces pulling on the wire from either end.
Force acting on an object due to gravity is,
Here, m is the mass of the object and g is acceleration due to gravity.
The expression for kinetic friction force acting on an object is,
Here, 
is the coefficient of kinetic friction and N is the normal force acting on the object.
Answer:
The following figure shows the forces acting on the blocks 1 and 2. The blocks are connected through a massless string and sliding down the incline with acceleration a.
Refer figure 1 and consider the block 1.
Balance the forces acting along the direction perpendicular to the inclined plane.
The friction force acting on block 1 is,
Refer figure 1 and consider the block 2.
Balance the forces acting along the direction perpendicular to the inclined plane.
The friction force acting on block 2 is,
