Work, Energy & Power · JEE Main previous year questions

2020 14 questions

1. Q332020 · 6 Sept 2020 · Shift 1

   If the potential energy between two molecules is given by $$U=-\frac{A}{r^6}+\frac{B}{r^{12}},$$ then at equilibrium, separation between molecules, and the potential energy are :

   1. A.${\left(\frac{2B}{A}\right)}^{1/6},-\frac{A^2}{4B}$
   2. B.${\left(\frac{2B}{A}\right)}^{1/6},-\frac{A^2}{2B}$
   3. C.${\left(\frac{B}{A}\right)}^{1/6},0$
   4. D.${\left(\frac{B}{2A}\right)}^{1/6},-\frac{A^2}{2B}$
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   Answer: A

2. Q462020 · 6 Sept 2020 · Shift 1· Numerical answer

   Two bodies of the same mass are moving with the same speed, but in different directions in a plane. They have a completely inelastic collision and move together thereafter with a final speed which is half of their initial speed. The angle between the initial velocities of the two bodies (in degree) is ________.

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   Answer: 120

3. Q332020 · 6 Sept 2020 · Shift 2

   In a dilute gas at pressure P and temperature T, the mean time between successive collisions of a molecule varies with T as :

   1. A.$\sqrt{T}$
   2. B.$T$
   3. C.$\frac{1}{T}$
   4. D.$\frac{1}{\sqrt{T}}$
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   Answer: D

4. Q342020 · 6 Sept 2020 · Shift 2

   When a particle of mass m is attached to a vertical spring of spring constant k and released, its motion is described by $y(t)=y_0{\sin }^2\omega t$, where 'y' is measured from the lower end of unstretched spring. Then $\omega$ is:

   1. A.$\sqrt{\frac{g}{y_0}}$
   2. B.$\frac{1}{2}\sqrt{\frac{g}{y_0}}$
   3. C.$\sqrt{\frac{2g}{y_0}}$
   4. D.$\sqrt{\frac{g}{2y_0}}$
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   Answer: D

5. Q292020 · 3 Sept 2020 · Shift 1

   When the wavelength of radiation falling on a metal is changed from 500 nm to 200 nm, the maximum kinetic energy of the photoelectrons becomes three times larger. The work function of the metal is close to :

   1. A.1.02 eV
   2. B.0.81 eV
   3. C.0.61 eV
   4. D.0.52 eV
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   Answer: C

6. Q352020 · 3 Sept 2020 · Shift 2

   A block of mass 1.9 kg is at rest at the edge of a table, of height 1 m. A bullet of mass 0.1 kg collides with the block and sticks to it. If the velocity of the bullet is 20 m/s in the horizontal direction just before the collision then the kinetic energy just before the combined system strikes the floor, is [Take $g=10m/{\mathrm{s}}^2$. Assume there is no rotational motion and loss of energy after the collision is negligible.]

   1. A.23 J
   2. B.21 J
   3. C.20 J
   4. D.19 J
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   Answer: B

7. Q402020 · 2 Sept 2020 · Shift 1

   A particle of mass m with an initial velocity $u\hat{i}$ collides perfectly elastically with a mass 3 m at rest. It moves with a velocity $v\hat{j}$ after collision, then, v is given by :

   1. A.$v=\sqrt{\frac{2}{3}}u$
   2. B.$v=\frac{u}{\sqrt{3}}$
   3. C.$v=\frac{u}{\sqrt{2}}$
   4. D.$v=\frac{1}{\sqrt{6}}u$
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   Answer: C

8. Q482020 · 2 Sept 2020 · Shift 2· Numerical answer
   
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   Answer: 10

9. Q272020 · 9 Jan 2020 · Shift 1
   
   1. A.2
   2. B.$\frac{1}{2}$
   3. C.1
   4. D.$\frac{3}{2}$
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   Answer: C

10. Q282020 · 9 Jan 2020 · Shift 1

    A body A of mass $m$ is moving in a circular orbit of radius $R$ about a planet. Another body B of mass $\frac{m}{2}$ collides with A with a velocity which is half $\left(\frac{\vec{v}}{2}\right)$ the instantaneous velocity $\vec{v}$ of A. The collision is completely inelastic. Then, the combined body :

    1. A.starts moving in an elliptical orbit around the planet.
    2. B.Falls vertically downwards towards the planet
    3. C.Escapes from the Planet's Gravitational field.
    4. D.continues to move in a circular orbit
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    Answer: A

11. Q382020 · 9 Jan 2020 · Shift 1

    Two particles of equal mass m have respective initial velocities $u\hat{i}$ and $u\left(\frac{\hat{i}+\hat{j}}{2}\right)$. They collide completely inelastically. The energy lost in the process is :

    1. A.$\frac{1}{3}m{u}^2$
    2. B.$\frac{1}{8}m{u}^2$
    3. C.$\frac{3}{4}m{u}^2$
    4. D.$\sqrt{\frac{2}{3}}m{u}^2$
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    Answer: B

12. Q292020 · 8 Jan 2020 · Shift 1
    
    1. A.
    2. B.
    3. C.
    4. D.
    Show answer

    Answer: B

13. Q482020 · 8 Jan 2020 · Shift 1· Numerical answer

    A body A, of mass $m=0.1\text{ kg}$ has an initial velocity of $3\hat{i}{\text{ ms}}^{-1}$. It collides elastically with another body, B of the same mass which has an initial velocity of $5\hat{j}{\text{ ms}}^{-1}$. After collision, A moves with a velocity $\vec{v}=4\left(\hat{i}+\hat{j}\right)$. The energy of B after collision is written as $\frac{x}{10}$. The value of x is _______.

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    Answer: 1

14. Q402020 · 8 Jan 2020 · Shift 2

    A uniform sphere of mass 500 g rolls without slipping on a plane horizontal surface with its centre moving at a speed of 5.00 cm/s. Its kinetic energy is :

    1. A.$8.75\times 10^{-3}\text{ J}$
    2. B.$1.13\times 10^{-3}\text{ J}$
    3. C.$8.75\times 10^{-4}\text{ J}$
    4. D.$6.25\times 10^{-4}\text{ J}$
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    Answer: C