Theory question 108
VectorsThe position vector of a body, with respect to the origin, is given by r = 4t i + (12 − 3t) j at anytime t seconds. (a) Find the velocity of the body (b) Calculate the magnitude of the displacement between t = 0 and t = 5.
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Model answer
(a) v = dr/dt = 4i − 3j (speed 5 ms−1)
(b) r(0) = 12j, r(5) = 20i − 3j
Displacement = 20i − 15j
Magnitude = √(400 + 225) = 25 m
Explanation
Displacement is the change in position vector, not the difference of the two distances from O.