Two 60 W bulbs are connected in series across 220 V. Each bulb power becomes (approximately) MCQ with Answer and Explanation
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Question #1
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The half-life of a substance is 2 years. After 6 years, what fraction of original substance remains?
Question #2
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A body of mass 2 kg is moving with an acceleration of 5 m/s². The rate of change of its momentum is:
Correct Answer: Option B
Explanation:
According to Newton's Second Law of Motion, the rate of change of momentum is directly proportional to the applied unbalanced force. Rate of change of momentum = Force = mass × acceleration. Force = 2 kg × 5 m/s² = 10 Newtons (N). Note that '10 kg m/s' is a unit of momentum, not its rate of change.
According to Newton's Second Law of Motion, the rate of change of momentum is directly proportional to the applied unbalanced force. Rate of change of momentum = Force = mass × acceleration. Force = 2 kg × 5 m/s² = 10 Newtons (N). Note that '10 kg m/s' is a unit of momentum, not its rate of change.
Question #3
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A body is thrown vertically upwards. At the highest point of its trajectory:
Correct Answer: Option C
Explanation:
At maximum height, vertical velocity becomes zero momentarily. However, acceleration due to gravity (g) acts downward throughout the motion, including at the peak. Thus acceleration is g ≈ 9.8 m/s² downward, not zero. Memory tip: 'Peak of projectile: v=0, a=g downward'. This conceptual question tests understanding of motion under gravity, frequently appearing in competitive exams. Always distinguish velocity (which changes) from acceleration (constant in free fall near Earth). Misconception that acceleration is zero at peak is a common trap.
At maximum height, vertical velocity becomes zero momentarily. However, acceleration due to gravity (g) acts downward throughout the motion, including at the peak. Thus acceleration is g ≈ 9.8 m/s² downward, not zero. Memory tip: 'Peak of projectile: v=0, a=g downward'. This conceptual question tests understanding of motion under gravity, frequently appearing in competitive exams. Always distinguish velocity (which changes) from acceleration (constant in free fall near Earth). Misconception that acceleration is zero at peak is a common trap.
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