Question

A 3000kg train is travelling 30m/s towards east. It collides with a 3500kg train with a velocity of 40m/s towards the west. The two trains combine at impact. Find the velocity of the combined trains.

Answer 1

Answer on Question #72868 Physics / Other

A $m = 3000$ kg train is travelling $u = 30$ m/s towards east. It collides with a $M = 3500$ kg train with a velocity of $v = 40$ m/s towards the west. The two trains combine at impact. Find the velocity $V$ of the combined trains.

Solution:

Let the direction toward the west is positive. The law of conservation of momentum gives

$$-mu + Mv = (m + M)V$$

Thus

$$V = \frac{-mu + Mv}{m + M}$$ $$V = \frac{-3000 \times 30 + 3500 \times 40}{3000 + 3500} = 7.7 \text{ m/s}$$

Answer: $7.7 \text{ m/s}$ toward the west.

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