A bullet of mass 20 g travelling horizontally with a velocity of 100 m/s strikes a wooden block and comes to rest in 0.05 s. Calculate the magnitude of force in N exerted by the wooden block on the bullet.

Mass of bullet (m)= 20 g = 0.02 kg

Initial velocity of bullet (u) =100 m/s

             Final velocity of bullet (V) = 0

             Time (t)= 0.05 seconds

             Acceleration on the bullet (a)?

             Force acting on wooden block (F) = ?

             Distance penetrated by bullet (s) = ?

             We know;

Step 1: Calculate the acceleration of the v = u + at

  0= 100+ a ×0.05

                          – a × 0.05 = 100

                    a = -2000 ms-2

Step 2: Calculate the distance of penetration using s = ut + ½ at2

                                       = 100 × 0.05 +   0.5 x (–2000) × (0.05)2

                            = 7.5 m

  We know,  F = ma

             Force acting on bullet (F)

                                        = 0.02 × (– 2000) = -40N

          Negative sign denotes that wooden block exerts force in the direction, opposite to the direction of motion of the bullet.

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