Question

A block of mass 3 kg slides along a horizontal surface that has negligible friction except for one section, as shown above. The block arrives at the rough section with a speed of 5 m/s and leaves it 0.5 s later with a speed of 3 m/s.

Answer 1

Complete Question

The complete question is shown on the first uploaded image

Answer:

The value  is $F_f = 3 * -4$

Explanation:

From the question we are told that  

  The mass of the block is  $m = 3 \ kg$

  The initial speed of the block before entering the rough section is $u = 5 \ m/s$

  The time taken is  t = 0.5 s

   The  speed with which the block leaves the rough section is  $v = 3 \ m/s$

Generally from kinematic equation

      $v = u + at$

=>   $a = \frac{v - u }{t}$

=>   $a = \frac{3 - 5 }{0.5}$

=>   $a = - 4$

Generally the magnitude of the average frictional  force is mathematically represented as

      $F_f = m * a$

=>  $F_f = 3 * -4$

=>    $F_f = -12 \ N$

The negative sign show that the force is acting in the opposite direction to the direction of motion of the block