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A ball of mass 0.5kg moving at 10ms⁻¹ collides with…

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A ball of mass 0.5kg moving at 10ms⁻¹ collides with another ball of equal mass at rest. If the two balls move off together after the impact, calculate their common velocity.

A. 0.2ms⁻¹

B. 0.5ms⁻¹

C. 5.0ms⁻¹

D. 5.5ms⁻¹




Please note that momentum before impact must be = momentum after impact. This is the law of conservation of momentum.

Data given:

Mass of ball 1 (M₁) = 0.5kg

Mass of ball 2 (M₂) = 0.5kg

Velocity of ball 1 before collision (V₁) = 10 ms⁻¹

Velocity of ball 2 before collision (V₂) = 0 (since we were told it was at rest)

Common velocity after impact (V₃) =?

Total momentum before impact

 = M₁V₁ + M₂V₂

= (0.5 × 10) + (0.5 × 0)

= 5 + 0

= 5kgm/s

Total momentum after impact

= (M₁ + M₂)V₃ (since they sticked together after impact)

= (0.5 + 0.5)V₃

= (1)V₃

= V₃

If momentum before impact = momentum after impact, then

5 = V₃

V₃ = 5m/s

Now for the right answer to the above question:

  1. Option A is incorrect.
  2. Option B is incorrect.
  3. C is correct.
  4. D is not the correct answer.


You may please note these/this:

  • The law of conservation of momentum is important here.
  • Total momentum before impact = total momentum after impact.
  • A body at rest has a velocity of zero.
  • If the bodies stick together after the collision, the new mass becomes equal to the simple addition of the masses coming together.

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/ culled from 2021 JAMB-UTME PHYSICS question 4 /

1 Answers

  1. +1 Votes Thumb up 0 Votes Thumb down 0 Votes

    Total momentum before impact = total momentum after impact

    Admin - Mar 22, 2022 | Reply

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