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A bus travels north along a straight road at a constant speed of 50 km/h and then takes a 90° turn. If its speed does not change after the turn, the change in the bus’s velocity during the turn is

1. 70.7 km/h toward the south-west
2. 70.7 km/h toward the north-west
3. 50 km/h toward the west
4. No change

Correct answer: 70.7 km/h toward the south-west

Solution

Initial velocity 50 km/h north, final 50 km/h (after 90 deg turn, e.g. west). Change = vf - vi = (west) + (-north), a vector of magnitude sqrt(50^2 + 50^2) = 70.7 km/h directed toward the south-west (not north-west, since we subtract the original northward velocity).

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