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A ball is dropped from rest from the top of a building of height ‘h’. At the same instant, a second ball is projected vertically upward from ground level, such that it has zero speed when it reaches the top of the building. When the two balls pass each other, which ball has the greater speed, or do they have same speed? Where will two balls be when they are alongside each other? At height h/2,or above or below of this height?

A ball is dropped from rest from the top of a building of height ‘h’. At the same instant, a second ball is projected vertically upward from ground level, such that it has zero speed when it reaches the top of the building. When the two balls pass each other, which ball has the greater speed, or do they have same speed? Where will two balls be when they are alongside each other? At height h/2,or above or below of this height?

Grade:11

1 Answers

Sumit Majumdar IIT Delhi
askIITians Faculty 137 Points
8 years ago
Dear student,
The total time taken by the ball would be equal to
T=\frac{u}{g}
Here, u is the initial velocity of the ball when projected from the ground. This would also be equal to the final velocity of the ball when it is coming from the top of the building.
Hence, when both the balls cross each other, their velocities are equal and acting in opposite directions. And this results into the height achieved by both the particles to be equal and that is half the total height.
Regards

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