A lead bullet of mass 0.05 kg is fired with a speed of 200 m/s

PHYSICS
WAEC 2023

A lead bullet of mass 0.05 kg is fired with a speed of 200 m/s into a lead block of mass 0.95 kg at rest. Given that the lead block moves after the impact, determine its kinetic energy.

  • A. 150J
  • B. 200J
  • C. 50J
  • D. 100J

Correct Answer: C. 50J

Explanation

\(M_{bullet}\) = 0.05kg, \(V_{bullet}\) = 200m/s, \(M_{block}\) = 0.95kg and \(V_{block}\) = 0

for an inelastic collision

\(M_{bullet} \times V_{bullet} + M_{block} \times V_{block} = (M_{bullet} + M_{block})\)v

0.05 x 200 + 0.95 x 0 = ( 0.05 + 0.95)v

10 + 0 = v

v = 10m/s

K.E of the block = \(\frac{1}{2}mv^2\)

K . E = \(\frac{1}{2} \times(0.05 + 0.95) \times10^2\) ( bullet now part of the block)

K . E = \(\frac{1}{2} \times1 \times100\)

= 50J



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