A stone dropped from a helicopter passes a tall vertical glass building. It takes 2 s to cross the entire height of the building. The velocity of the stone at the bottom of the building is exactly three times its velocity at the top of the building. Find the height of the building. (Take g = 10 m s ⁻² )

Step-by-step solution

Let the velocity of the stone at the top of the building be u . The velocity at the bottom of the building is given as v = 3u . Using the first equation of motion, v = u + gt for the motion across the building: 3u = u + (10)(2) 2u = 20 u = 10 m s ⁻¹ Now, use the second equation of motion to find the height of the building ( s ): s = ut + 1 2 gt^2 s = (10)(2) + 1 2 (10)(2)^2 s = 20 + 20 = 40 m Answer: 40 m