JEE Main 2015 · 4 Apr · Shift 1 · Physics Q12

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PhysicsSingle correct+4 / -1Question 12 of 90

For a simple pendulum, a graph is plotted between its kinetic energy (KE) and potential energy (PE) against its displacement d. Which one of the following represents these correctly ?

(graphs are schematic and not drawn to scale)

KE an upward parabola (minimum at d = 0); PE a downward dashed parabola

Graph of energy E against displacement d: KE is a U-shaped parabola with its minimum at the origin; PE (dashed) is an inverted parabola.

KE a downward parabola (maximum at d = 0); PE an upward dashed parabola

Graph of energy E against displacement d: KE is an inverted parabola with its maximum at d = 0; PE (dashed) is a U-shaped parabola, zero at d = 0.

KE an upward parabola above the axis; PE a downward parabola below the axis

Graph of energy E against displacement d: KE is a U-shaped curve above the d-axis; PE (dashed) is an inverted curve below the axis.

KE and PE as straight-sided peaks meeting at d = 0

Graph of energy E against displacement d: KE and PE (dashed) are cusped curves crossing each other, KE peaked at d = 0.

Answer and worked solution

Official answer: B

$PE=\frac12kd^2$ (a U-shaped parabola, zero at $d=0$ ) and $KE=\frac12k(A^2-d^2)$ (an inverted parabola, maximum at $d=0$ ). Both are non-negative and they meet at the turning points. That is graph (2).

Topics:Energy in SHM

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JEE Main 2015 · 4 Apr · Shift 1, Physics question 12