CBSEGrade 11PhysicsChapter 4: Laws of Motion

A Box in Free Fall?

A box is dropped from a height of 100 meters above the ground. Considering air resistance to be negligible, calculate the time taken for the box to hit the ground. Additionally, consider the scenario where the box is dropped from a height of 50 meters. What implications does this have on the time taken for the box to hit the ground in both cases?

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📌 CONCEPT: The time taken for an object to hit the ground when dropped from a certain height is independent of the object's mass and depends only on the acceleration due to gravity and the initial height from which it is dropped.

📐 RULE / FORMULA: We can use the equation for free fall, which is given by: h = (1/2)gt^2, where h is the initial height, g is the acceleration due to gravity (approximately 9.8 m/s^2), and t is the time taken for the object to hit the ground.

💡 WORKED EXAMPLE: Suppose we have a box dropped from a height of 100 meters. We can rearrange the equation to solve for t: t = sqrt(2h/g) = sqrt(2*100/9.8) ≈ 3.2 seconds.

⚠️ COMMON MISTAKE: Students often forget to consider the direction of the acceleration due to gravity, which is downwards, and also neglect to use the correct value of g for the given location. Additionally, they might incorrectly use the equation for the range of a projectile instead of the equation for free fall.

21 Sept 26