Q18 of 25 Page 130

An object is dropped from rest at the height of 150 m, and another object is dropped from rest at a height of100 m. What is the difference in their height after 2 sec if both the object drop with the same acceleration? How does the difference in heights vary with time?

For object A

Initial velocity = u = 0m/s


Height = h = 150m


According to 3rd equation of motion


v2 = u2 + 2gh


v2 = 02 + 2(9.8)(150)


v2 = 19.6 × 150


v2 = 2940


v = 54.2m/s


According to 2nd equation of motion


s = ut + 1/2 gt2


s = 0 + 1/2 (9.8)(2)2


s = (9.8)(2)


s = 19.6m


Distance between object and ground = 150 – 19.6 = 130.4m


For object B


Initial velocity = u = 0m/s


Height = h = 100m


According to 3rd equation of motion


v2 = u2 + 2gh


v2 = 02 + 2(9.8)(100)


v2 = 19.6 × 100


v2 = 1960


v = 44.2 m/s


According to 2nd equation of motion


s = ut + 1/2 gt2


s = 0 + 1/2(9.8)(2)2


s = (9.8)(2)


s = 19.6m


Distance between object and ground = 100 – 19.6 = 80.4m


Distance between the two objects after 2s = 130.4 – 80.4


= 50m


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