Laws of Motion & Friction · JEE Main previous year questions

2020 11 questions

1. Q392020 · 6 Sept 2020 · Shift 1

   An insect is at the bottom of a hemispherical ditch of radius $1\text{ m}$. It crawls up the ditch but starts slipping after it is at height h from the bottom. If the coefficient of friction between the ground and the insect is 0.75, then h is : $(g=10\mathrm{m}{\mathrm{s}}^{-2})$

   1. A.$0.45\text{ m}$
   2. B.$0.60\text{ m}$
   3. C.$0.20\text{ m}$
   4. D.$0.80\text{ m}$
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   Answer: C

2. Q452020 · 6 Sept 2020 · Shift 2

   Given the masses of various atomic particles $m_p=1.0072\text{ u}$, $m_n=1.0087\text{ u}$, $m_e=0.000548\text{ u}$, $m_{\bar{\nu }}=0$, $m_d=2.0141\text{ u}$, where $\mathrm{p}\equiv \mathrm{proton}$, $\mathrm{n}\equiv \mathrm{neutron}$, $\mathrm{e}\equiv \mathrm{electron}$, $\bar{\nu }\equiv \text{antineutrino}$ and $\mathrm{d}\equiv \mathrm{deuteron}$. Which of the following process is allowed by momentum and energy conservation?

   1. A.$\mathrm{n}+\mathrm{n}\to \text{deuterium atom}$ (electron bound to the nucleus)
   2. B.$\mathrm{n}+\mathrm{p}\to \mathrm{d}+\gamma$
   3. C.$\mathrm{p}\to \mathrm{n}+{\mathrm{e}}^{+}+\bar{\nu }$
   4. D.${\mathrm{e}}^{+}+{\mathrm{e}}^{-}\to \gamma$
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   Answer: B

3. Q402020 · 3 Sept 2020 · Shift 1
   
   1. A.$63^{\circ }$
   2. B.$69^{\circ }$
   3. C.$55^{\circ }$
   4. D.$49^{\circ }$
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   Answer: A

4. Q482020 · 3 Sept 2020 · Shift 2· Numerical answer

   A block starts moving up an inclined plane of inclination $30^{\circ }$ with an initial velocity of $v_0$. It comes back to its initial position with velocity $\frac{v_0}{2}$. The value of the coefficient of kinetic friction between the block and the inclined plane is close to $\frac{I}{1000}$. The nearest integer to I is _______.

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   Answer: 346

5. Q302020 · 2 Sept 2020 · Shift 1

   Two identical strings X and Z made of same material have tension ${\mathrm{T}}_{\mathrm{X}}$ and ${\mathrm{T}}_{\mathrm{Z}}$ in them. If their fundamental frequencies are 450 Hz and 300 Hz, respectively, then the ratio ${\mathrm{T}}_{\mathrm{X}}/{\mathrm{T}}_{\mathrm{Z}}$ is

   1. A.2.25
   2. B.0.44
   3. C.1.25
   4. D.1.5
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   Answer: A

6. Q312020 · 2 Sept 2020 · Shift 1
   
   1. A.$2\sqrt{2gC}$
   2. B.$2\sqrt{gC}$
   3. C.$\sqrt{\frac{2gC}{ab}}$
   4. D.$\sqrt{\frac{2g}{C}}$
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   Answer: A

7. Q322020 · 2 Sept 2020 · Shift 1
   
   1. A.0.5 mg
   2. B.2 mg
   3. C.0.75 mg
   4. D.1 mg
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   Answer: D

8. Q472020 · 2 Sept 2020 · Shift 1· Numerical answer
   
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   Answer: 3

9. Q262020 · 7 Jan 2020 · Shift 1

   A 60 HP electric motor lifts an elevator having a maximum total load capacity of 2000 kg. If the frictional force on the elevator is 4000 N, the speed of the elevator at full load is close to : (1 HP = 746 W, $g=10{\text{ ms}}^{-2}$)

   1. A.$1.5{\text{ ms}}^{-1}$
   2. B.$1.7{\text{ ms}}^{-1}$
   3. C.$2.0{\text{ ms}}^{-1}$
   4. D.$1.9{\text{ ms}}^{-1}$
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   Answer: D

10. Q372020 · 7 Jan 2020 · Shift 1
    
    1. A.$r\sqrt{\frac{3}{2gh}}$
    2. B.$r\sqrt{\frac{3}{4gh}}$
    3. C.$\frac{1}{r}\sqrt{\frac{4gh}{3}}$
    4. D.$\frac{1}{r}\sqrt{\frac{2gh}{3}}$
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    Answer: C

11. Q462020 · 7 Jan 2020 · Shift 2· Numerical answer
    
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    Answer: 50