A block (mass 5 kg ) sits at rest. A second block (mass 10 kg ) collides with the first block, initially moving with a speed of 12 m/s just before the collision. After the collision, the two blocks stick together, and they slide for 4 s across a rough surface before coming to a stop. What was the magnitude of the average force of friction acting on the blocks after the collision?

The magnitude of the average force of friction acting on the blocks after the collision is 30 N.

Explanation:

According to the conservation of momentum,

Putting the given values into the above formula as follows.

          m/s

We assume that acceleration due to friction is . Also,

           v = u + at

Here,  v = 0 m/s

          u = 8 m/s

          t = 4 sec

Then, value of acceleration will be as follows.

           v = u + at

       a = 2

Now, we know that expression for frictional force is as follows.      

               =

              = 30 N

Thus, we can conclude that the magnitude of the average force of friction acting on the blocks after the collision is 30 N.

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