A stone is thrown horizontally from the top of a 20 m high building with a speed of 12 m/s. It hits the ground at a distance R from the building. Taking g = 10 m/s2 and neglecting air resistance will give :

This is a problem of horizontal projectile motion. To find the horizontal distance (Range R), we must first determine the time of flight.

• Vertical Motion: The stone is thrown horizontally, so its initial vertical velocity is 0. Using the equation h = ut + ½gt², where h = 20 m and g = 10 m/s²:
  20 = 0 + ½(10)(t²)
  20 = 5t²
  t² = 4, which gives t = 2 seconds.
• Horizontal Motion: Since air resistance is neglected, horizontal velocity remains constant at 12 m/s. The range is calculated as:
  R = Horizontal Speed × Time
  R = 12 m/s × 2 s = 24 m.

Thus, the stone hits the ground at a distance of 24 m from the building, confirming Option C as the correct answer.