Work, Energy & Power · JEE Main previous year questions

2021 12 questions

1. Q552021 · 1 Sept 2021 · Shift 2· Numerical answer

   The average translational kinetic energy of ${\mathrm{N}}_2$ gas molecules at ____ ${}^{\circ }\mathrm{C}$ becomes equal to the K.E. of an electron accelerated from rest through a potential difference of $0.1\mathrm{volt}$. (Given ${\mathrm{k}}_{\mathrm{B}}=1.38\times 10^{-23}J/K$) (Fill the nearest integer).

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   Answer: 500

2. Q592021 · 1 Sept 2021 · Shift 2· Numerical answer

   An engine is attached to a wagon through a shock absorber of length $1.5\mathrm{m}$. The system with a total mass of $40,000\mathrm{kg}$ is moving with a speed of $72\mathrm{km}{\mathrm{h}}^{-1}$ when the brakes are applied to bring it to rest. In the process of the system being brought to rest, the spring of the shock absorber gets compressed by $1.0\mathrm{m}$. If 90% of energy of the wagon is lost due to friction, the spring constant is ____ $\times 10^{5}N/m$.

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   Answer: 16

3. Q512021 · 27 Jul 2021 · Shift 2· Numerical answer
   
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   Answer: 9

4. Q332021 · 25 Jul 2021 · Shift 1

   What should be the order of arrangement of de-Broglie wavelength of electron (${\lambda }_e$), an $\alpha$-particle (${\lambda }_a$) and proton (${\lambda }_p$) given that all have the same kinetic energy?

   1. A.${\lambda }_e={\lambda }_p={\lambda }_{\alpha }$
   2. B.${\lambda }_e<{\lambda }_p<{\lambda }_{\alpha }$
   3. C.${\lambda }_e>{\lambda }_p>{\lambda }_{\alpha }$
   4. D.${\lambda }_e={\lambda }_p>{\lambda }_{\alpha }$
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   Answer: C

5. Q512021 · 25 Jul 2021 · Shift 2· Numerical answer

   A system consists of two types of gas molecules A and B having same number density $2\times 10^{25}/{\mathrm{m}}^3$. The diameter of A and B are 10 $\mathring{A}$ and 5 $\mathring{A}$ respectively. They suffer collision at room temperature. The ratio of average distance covered by the molecule A to that of B between two successive collision is ____ $\times 10^{-2}$

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   Answer: 25

6. Q562021 · 25 Jul 2021 · Shift 2· Numerical answer

   A force of $F=(5y+20)\hat{j}$ N acts on a particle. The work done by this force when the particle is moved from y = 0 m to y = 10 m is ____ J.

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   Answer: 450

7. Q522021 · 20 Jul 2021 · Shift 1· Numerical answer
   
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   Answer: 1

8. Q472021 · 18 Mar 2021 · Shift 1

   A constant power delivering machine has towed a box, which was initially at rest, along a horizontal straight line. The distance moved by the box in time 't' is proportional to :-

   1. A.$t^{2/3}$
   2. B.$t^{3/2}$
   3. C.$t$
   4. D.$t^{1/2}$
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   Answer: B

9. Q332021 · 18 Mar 2021 · Shift 2

   An object of mass $m_1$ collides with another object of mass $m_2$, which is at rest. After the collision the objects move with equal speeds in opposite direction. The ratio of the masses $m_2:m_1$ is :

   1. A.$1:1$
   2. B.$3:1$
   3. C.$2:1$
   4. D.$1:2$
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   Answer: B

10. Q462021 · 26 Feb 2021 · Shift 1

    Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R. Assertion A : Body 'P' having mass M moving with speed 'u' has head-on collision elastically with another body 'Q' having mass 'm' initially at rest. If m << M, body 'Q' will have a maximum speed equal to '2u' after collision. Reason R : During elastic collision, the momentum and kinetic energy are both conserved. In the light of the above statements, choose the most appropriate answer from the options given below :

    1. A.A is correct but R is not correct.
    2. B.A is not correct but R is correct.
    3. C.Both A and R are correct and R is the correct explanation of A.
    4. D.Both A and R are correct but R is NOT the correct explanation of A.
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    Answer: C

11. Q562021 · 26 Feb 2021 · Shift 2· Numerical answer

    27 similar drops of mercury are maintained at 10V each. All these spherical drops combine into a single big drop. The potential energy of the bigger drop is __________ times that of a smaller drop.

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    Answer: 243

12. Q372021 · 25 Feb 2021 · Shift 2

    Given below are two statements : Statement I : In a diatomic molecule, the rotational energy at a given temperature obeys Maxwell's distribution. Statement II : In a diatomic molecule, the rotational energy at a given temperature equals the translational kinetic energy for each molecule. In the light of the above statements, choose the correct answer from the options given below :

    1. A.Both Statement I and Statement II are true
    2. B.Both Statement I and Statement II are false
    3. C.Statement I is true but Statement II is false.
    4. D.Statement I is false but Statement II is true.
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    Answer: C