A body is moving with uniform speed in a circular path. Which statement is correct?
A. Velocity is constant
B. Acceleration is zero
C. Acceleration is directed towards the center
D. No force acts on the body
Answer: Option C
Solution (By JKSSB Mock Tests)
In uniform circular motion, speed is constant but velocity direction changes continuously, requiring centripetal acceleration directed toward the center (a = v²/r). By Newton's second law, a centripetal force must act. Velocity isn't constant (direction changes); acceleration isn't zero; force is required. Memory tip: 'Uniform circular motion: constant speed, changing velocity, center-seeking acceleration'. This conceptual question tests understanding of circular dynamics, crucial for mechanics in competitive exams. Always distinguish speed (scalar) from velocity (vector) in motion analysis.
Explanation:
Resistance R = ρL/A. Volume constant: A ∝ 1/L. Stretching length to 2L reduces area to A/2. New R' = ρ(2L)/(A/2) = 4ρL/A = 4R = 40 Ω. Resistance proportional to (length)² when volume constant.
Explanation:
When an elevator moves downwards with acceleration 'a', the net downward force on the person is mg - R = ma, where R is the normal reaction (apparent weight). Solving for R gives R = m(g - a). Since g - a is less than g, the apparent weight (R) is less than the true weight (mg).
Explanation:
At maximum height, vertical velocity = 0 momentarily, but acceleration = g downward throughout motion. Memory tip: 'Peak: v=0, a=g; gravity never switches off'. Kinematics concept frequently tested to correct misconception that acceleration vanishes at peak.
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