Two particles of equal mass have velocities v1 = 4 i and v2 = 4 j. The first particle has acceleration a1 = (5 i + 5 j) m/s² while the second particle has zero acceleration. The centre of mass of the two particles moves along a:

Straight line
Parabola
Circle
Ellipse

Correct answer: Straight line

Solution

v_cm = (4i+4j)/2 = 2i+2j and a_cm = (5i+5j)/2 = 2.5i+2.5j are both along the direction i+j (parallel), so the centre of mass moves in a straight line.

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