Two blocks of masses 10 kg and 30 kg are placed along a vertical line. The first block is raised through a height of 7 cm. By what distance should the second mass be moved to raise the centre of mass by 1 cm?

Shift y-coordinate of the 10kg block = 7 cm

Shift in y-coordinate of the 20kg block = y cm

Shift in y-coordinate of centre of mass of the system = 1 cm

∴ The 30kg block should be moved 1 cm downwards to raise the centre of mass through 1 cm upwards.