Q95 / 125 · BITSAT 2021 · Physics

Suppose the law of gravitational attraction suddenly changes and becomes an inverse cube law i.e. F $\propto \frac{1}{r^{3}}$, but still remaining a central force. Then

  • Correct answer
    A
    Kepler's law of area still holds
  • B
    Kepler's law of period still holds
  • C
    Kepler's law of area and period still holds
  • D
    neither the law of area, nor the law of period still holds

Solution

According to kepler's law of area $\frac{\mathrm{d} \mathrm{A}}{\mathrm{dt}}=\frac{\mathrm{L}}{2 \mathrm{~m}}$ For central forces, torque $=0$ $\therefore \mathrm{L}=$ constant $\therefore \frac{\mathrm{d} \mathrm{A}}{\mathrm{dt}}=$ constant

Hence, the correct answer is option: 'A'.

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