Work, Energy & Power · JEE Main previous year questions

2019 8 questions

1. Q422019 · 12 Apr 2019 · Shift 1

   A person of mass M is, sitting on a swing of length L and swinging with an angular amplitude ${\theta }_0$. If the person stands up when the swing passes through its lowest point, the work done by him, assuming that his center of mass moves by a distance $\ell (\ell \ll L)$, is close to;

   1. A.$mg\ell (1+{\theta }_0^2)$
   2. B.$mg\ell$
   3. C.$mg\ell \left(1+\frac{{\theta }_0^2}{2}\right)$
   4. D.$mg\ell (1-{\theta }_0^2)$
   Show answer

   Answer: A

2. Q492019 · 10 Apr 2019 · Shift 1

   A $25\times 10^{-3}{\mathrm{m}}^3$ volume cylinder is filled with 1 mol of ${\mathrm{O}}_2$ gas at room temperature (300K). The molecular diameter of ${\mathrm{O}}_2$, and its root mean square speed, are found to be 0.3 nm, and 200 m/s, respectively. What is the average collision rate (per second) for an ${\mathrm{O}}_2$ molecule ?

   1. A.$\sim 10^{13}$
   2. B.$\sim 10^{12}$
   3. C.$\sim 10^{11}$
   4. D.$\sim 10^{10}$
   Show answer

   Answer: D

3. Q542019 · 10 Apr 2019 · Shift 1
   
   1. A.6.5 m/s and 3.2 m/s
   2. B.6.5 m/s and 6.3 m/s
   3. C.3.2 m/s and 6.3 m/s
   4. D.3.2 m/s and 12.6 m/s
   Show answer

   Answer: B

4. Q382019 · 9 Apr 2019 · Shift 1
   
   1. A.$\frac{1}{4\pi {\epsilon }_0}\left[\frac{q^2}{d}+\frac{qQd}{D^2}\right]$
   2. B.$\frac{1}{4\pi {\epsilon }_0}\left[-\frac{q^2}{d}-\frac{qQd}{2D^2}\right]$
   3. C.$\frac{1}{4\pi {\epsilon }_0}\left[-\frac{q^2}{d}-\frac{qQd}{D^2}\right]$
   4. D.$\frac{1}{4\pi {\epsilon }_0}\left[-\frac{q^2}{d}+\frac{2qQd}{D^2}\right]$
   Show answer

   Answer: C

5. Q402019 · 9 Apr 2019 · Shift 1

   A body of mass 2 kg makes an elastic collision with a second body at rest and continues to move in the original direction but with one fourth of its original speed. What is the mass of the second body ?

   1. A.1.2 kg
   2. B.1.0 kg
   3. C.1.8 kg
   4. D.1.5 kg
   Show answer

   Answer: A

6. Q482019 · 12 Jan 2019 · Shift 1
   
   1. A.$1\mathrm{J}$
   2. B.$10\mathrm{J}$
   3. C.$5\mathrm{J}$
   4. D.$30\mathrm{J}$
   Show answer

   Answer: B

7. Q312019 · 12 Jan 2019 · Shift 2

   An ideal gas is enclosed in a cylinder at pressure of 2 atm and temperature 300 K. The mean time between two successive collisions is $6\times 10^{-8}\mathrm{s}$. If the pressure is doubled and temperature is increased to 500 K, the mean time between two successive collisions will be close to

   1. A.$0.5\times 10^{-8}\mathrm{s}$
   2. B.$4\times 10^{-8}\mathrm{s}$
   3. C.$3\times 10^{-6}\mathrm{s}$
   4. D.$2\times 10^{-7}\mathrm{s}$
   Show answer

   Answer: B

8. Q492019 · 9 Jan 2019 · Shift 1
   
   1. A.5
   2. B.2
   3. C.4
   4. D.3
   Show answer

   Answer: C