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WAEC Physics 2019 Paper

Question : 23

Total: 49

^{-1}

^{-1}

Solution:

Concept:

When two bodies stick together after collision, total momentum before collision equals total momentum of the combined mass after collision.

Explanation:

Since both cars move in the same direction, their momenta are added.

Momentum of first car =

800 \times 80 = 64000\ \text{kg km h}^{-1}

Momentum of second car =

1200 \times 40 = 48000\ \text{kg km h}^{-1}

Total initial momentum =

64000 + 48000 = 112000\ \text{kg km h}^{-1}

Combined mass after collision =

800 + 1200 = 2000\ \text{kg}

Using conservation of momentum:

112000 = 2000 \times V

V = \frac{112000}{2000} = 56\ \text{km h}^{-1}

Thus, the common velocity is

56\ \text{km h}^{-1}

Answer:

56\ \text{km h}^{-1}

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