A stone is thrown horizontally from the top of a cliff 45 m high. How long will

Practice Questions

Q1
A stone is thrown horizontally from the top of a cliff 45 m high. How long will it take to hit the ground? (Assume g = 10 m/s²)
  1. 3 s
  2. 4 s
  3. 5 s
  4. 6 s

Questions & Step-by-Step Solutions

A stone is thrown horizontally from the top of a cliff 45 m high. How long will it take to hit the ground? (Assume g = 10 m/s²)
  • Step 1: Identify the height of the cliff, which is 45 meters.
  • Step 2: Identify the acceleration due to gravity, which is given as g = 10 m/s².
  • Step 3: Use the formula for the height of an object in free fall: h = 0.5 * g * t².
  • Step 4: Rearrange the formula to solve for time (t): t = sqrt(2h/g).
  • Step 5: Substitute the values into the rearranged formula: t = sqrt(2 * 45 / 10).
  • Step 6: Calculate the value inside the square root: 2 * 45 = 90, and 90 / 10 = 9.
  • Step 7: Find the square root of 9: sqrt(9) = 3.
  • Step 8: Conclude that it will take 3 seconds for the stone to hit the ground.
  • Projectile Motion – The question tests understanding of the motion of an object under the influence of gravity, specifically how vertical motion is independent of horizontal motion.
  • Kinematic Equations – The use of the kinematic equation h = 0.5 * g * t^2 to calculate the time of fall based on height and acceleration due to gravity.
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