A ball of mass 5 kg is dropped from a height of 78.4 m. The time taken by the ball to hit the ground is:
Correct answer: B. 4s
- A. 2s
- B. 4s
- C. 8s
- D. 16s
Explanation
To solve this problem, we use the second equation of motion: S = ut + ½ gt2. Given data includes mass = 5 kg (not needed for time calculation), height (S) = 78.4 m, initial velocity (u) = 0 m/s, and acceleration due to gravity (g) = 9.8 m/s2. Substituting these values, the equation simplifies to 78.4 = 4.9t2. Solving for t2 gives t2 = 16, and taking the square root yields t = 4 seconds. Thus, the correct answer is 4 seconds. Options A (2s), C (8s), and D (16s) do not align with the reality of free-fall time from this height under Earth's gravity.
This question appeared on the ETEA MDCAT 2012 paper, which you can sit online with every answer explained.
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