Multiple choice

Bullets of mass 0.02 kg each, hit a plate at the rate of 300 bullets per second with a velocity of 50 ms-1 and reflect back with a velocity of 20 ms-1. The average force (in newton) acting on the plate is

  1. 420

  2. 480

  3. 180

  4. 222

  5. 360
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A Correct answer
Explanation

Change of momentum of one bullet = m(v - u) = 0.02Χ[50 - ( - 20)] = 1.4 kg ms-1Average force = rate of change of momentum of 300 bullets = 300 Χ 1.4 = 420 N

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