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Gravitation question

2021 · 16 Mar · Shift 1 · Q54
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  5. /2021 · 16 Mar · Shift 1 · Q54

Gravitation question

2021 · 16 Mar · Shift 1 · Q54

JEE MainPhysicsGravitationMCQ+4 / −1
The maximum and minimum distances of a comet from the Sun are 1.6 ×\times× 1012 m and 8.0 ×\times× 1010 m respectively. If the speed of the comet at the nearest point is 6 ×\times× 104 ms −-− 1, the speed at the farthest point is :
  1. A
    3.0 ×\times× 103 m/s
  2. B
    6.0 ×\times× 103 m/s
  3. C
    1.5 ×\times× 103 m/s
  4. D
    4.5 ×\times× 103 m/s
View written solutionFree

Correct answer: A

  1. Given data
  • Maximum distance from Sun (aphelion): ra=1.6×1012 mr_a = 1.6 \times 10^{12}\ \text{m}ra​=1.6×1012 m
  • Minimum distance from Sun (perihelion): rp=8.0×1010 mr_p = 8.0 \times 10^{10}\ \text{m}rp​=8.0×1010 m
  • Speed at nearest point: vp=6×104 m/sv_p = 6 \times 10^4\ \text{m/s}vp​=6×104 m/s
  • Speed at farthest point: va=?v_a = ?va​=?
  1. Use conservation of angular momentum

For motion under gravitational force, angular momentum is conserved. At nearest and farthest points, velocity is perpendicular to radius vector, so:

mrpvp=mravam r_p v_p = m r_a v_amrp​vp​=mra​va​

Cancelling mmm:

rpvp=ravar_p v_p = r_a v_arp​vp​=ra​va​

Thus,

va=rpvprav_a = \frac{r_p v_p}{r_a}va​=ra​rp​vp​​

  1. Substitute the values

va=(8.0×1010)(6×104)1.6×1012v_a = \frac{(8.0 \times 10^{10})(6 \times 10^4)}{1.6 \times 10^{12}}va​=1.6×1012(8.0×1010)(6×104)​

First simplify the numerical factor:

8.0×61.6=481.6=30\frac{8.0 \times 6}{1.6} = \frac{48}{1.6} = 301.68.0×6​=1.648​=30

Now powers of 10:

1010×104÷1012=1014−12=10210^{10} \times 10^4 \div 10^{12} = 10^{14-12} = 10^21010×104÷1012=1014−12=102

So,

va=30×102=3.0×103 m/sv_a = 30 \times 10^2 = 3.0 \times 10^3\ \text{m/s}va​=30×102=3.0×103 m/s

  1. Match with the options

3.0×103 m/s3.0 \times 10^3\ \text{m/s}3.0×103 m/s

So the correct option is A.

  1. Comparison with stored answer

Stored correct answer: A

Derived answer: A

They match.

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