Work, Energy & Power · JEE Main previous year questions

A spherical body of mass $2\mathrm{kg}$ starting from rest acquires a kinetic energy of $10000\mathrm{J}$ at the end of $5^{\text{th}}$ second. The force acted on the body is ____ $\mathrm{N}$.

A ball is projected with kinetic energy E, at an angle of $60^{\circ }$ to the horizontal. The kinetic energy of this ball at the highest point of its flight will become :

1. A.Zero
2. B.$\frac{E}{2}$
3. C.$\frac{E}{4}$
4. D.$\mathrm{E}$

The kinetic energy of emitted electron is $\mathrm{E}$ when the light incident on the metal has wavelength $\lambda$. To double the kinetic energy, the incident light must have wavelength:

1. A.$\frac{\mathrm{hc}}{\mathrm{E}\lambda -\mathrm{hc}}$
2. B.$\frac{\mathrm{hc}\lambda }{\mathrm{E}\lambda +\mathrm{hc}}$
3. C.$\frac{\mathrm{h}\lambda }{\mathrm{E}\lambda +\mathrm{hc}}$
4. D.$\frac{\mathrm{hc}\lambda }{\mathrm{E}\lambda -\mathrm{hc}}$

An object of mass $1\mathrm{kg}$ is taken to a height from the surface of earth which is equal to three times the radius of earth. The gain in potential energy of the object will be [If, $g=10\mathrm{m}{\mathrm{s}}^{-2}$ and radius of earth $=6400\mathrm{km}$ ]

1. A.$48\mathrm{MJ}$
2. B.$24\mathrm{MJ}$
3. C.$36\mathrm{MJ}$
4. D.$12\mathrm{MJ}$

1. A.$45\text{ m}$
2. B.$90\text{ m}$
3. C.$125\text{ m}$
4. D.$25\text{ m}$

1. A.
2. B.
3. C.
4. D.

Two cylindrical vessels of equal cross-sectional area $16{\text{ cm}}^2$ contain water upto heights $100\text{ cm}$ and $150\text{ cm}$ respectively. The vessels are interconnected so that the water levels in them become equal. The work done by the force of gravity during the process, is [Take, density of water $=10^3{\text{ kg/m}}^3$ and $g=10{\text{ ms}}^{-2}$ ] :

1. A.$0.25\text{ J}$
2. B.$1\text{ J}$
3. C.$8\text{ J}$
4. D.$12\text{ J}$

A monoatomic gas at pressure $P$ and volume $V$ is suddenly compressed to one eighth of its original volume. The final pressure at constant entropy will be :

1. A.$P$
2. B.$8P$
3. C.$32P$
4. D.$64P$

1. A.$\frac{v}{2\sqrt{2}}$
2. B.$\frac{v}{2}$
3. C.$\frac{v}{4}$
4. D.$\frac{v}{\sqrt{2}}$

A bag of sand of mass $9.8\text{ kg}$ is suspended by a rope. A bullet of $200\text{ g}$ travelling with speed $10{\text{ ms}}^{-1}$ gets embedded in it, then loss of kinetic energy will be :

1. A.$4.9\text{ J}$
2. B.$9.8\text{ J}$
3. C.$14.7\text{ J}$
4. D.$19.6\text{ J}$

A cyclotron is working at a frequency of $10\text{ MHz}$. If the radius of its dees is $60\text{ cm}$. The maximum kinetic energy of accelerated proton will be : (Take : $e=1.6\times 10^{-19}\text{ C}$, $m_p=1.67\times 10^{-27}\text{ kg}$)

1. A.$7.4\text{ MeV}$
2. B.$14.86\text{ MeV}$
3. C.$7.4\text{ GeV}$
4. D.$704\text{ GeV}$

Eight similar drops of mercury are maintained at 12 V each. All these spherical drops combine into a single big drop. The potential energy of bigger drop will be ____________ E. Where E is the potential energy of a single smaller drop.

What percentage of kinetic energy of a moving particle is transferred to a stationary particle when it strikes the stationary particle of 5 times its mass? (Assume the collision to be head-on elastic collision)

1. A.50.0%
2. B.66.6%
3. C.55.6%
4. D.33.3%

1. A.${\mathrm{W}}_3>{\mathrm{W}}_2>{\mathrm{W}}_1>{\mathrm{W}}_4$
2. B.${\mathrm{W}}_3>{\mathrm{W}}_2>{\mathrm{W}}_4>{\mathrm{W}}_1$
3. C.${\mathrm{W}}_2>{\mathrm{W}}_3>{\mathrm{W}}_4>{\mathrm{W}}_1$
4. D.${\mathrm{W}}_2>{\mathrm{W}}_3>{\mathrm{W}}_1>{\mathrm{W}}_4$

A flask contains argon and oxygen in the ratio of 3 : 2 in mass and the mixture is kept at $27^{\circ }\text{C}$. The ratio of their average kinetic energy per molecule respectively will be :

1. A.3 : 2
2. B.9 : 4
3. C.2 : 3
4. D.1 : 1

A $0.5\text{ kg}$ block moving at a speed of $12{\text{ ms}}^{-1}$ compresses a spring through a distance $30\text{ cm}$ when its speed is halved. The spring constant of the spring will be $\underline{}{\text{ Nm}}^{-1}$.

Potential energy as a function of r is given by $U=\frac{A}{r^{10}}-\frac{B}{r^5}$, where r is the interatomic distance, A and B are positive constants. The equilibrium distance between the two atoms will be :

1. A.${\left(\frac{A}{B}\right)}^{\frac{1}{5}}$
2. B.${\left(\frac{B}{A}\right)}^{\frac{1}{5}}$
3. C.${\left(\frac{2A}{B}\right)}^{\frac{1}{5}}$
4. D.${\left(\frac{B}{2A}\right)}^{\frac{1}{5}}$

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).

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 ____ $\times 10^{5}N/m$.

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.${\lambda }_e={\lambda }_p>{\lambda }_{\alpha }$

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 ____ $\times 10^{-2}$

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.