JEE Main 2020 Question Paper (07-Jan-2020) (Shift 1)

Question 1

$A$ litre of dry air at STP expands adiabatically to a volume of $3$ litres. If $\gamma = 1.40$, the work done by air is: $\left(3^{1.4} = 4.6555\right)$. [Take air to be an ideal gas]

Accepted Answer

$90.5 \mathrm{J}$

Answer

$60.7 \mathrm{J}$

Answer

$100.8 \mathrm{J}$

Answer

$48 \mathrm{J}$

Question 2

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

Accepted Answer

$1.9 \mathrm{m} \mathrm{s}^{-1}$

Answer

$1.7 \mathrm{m} \mathrm{s}^{-1}$

Answer

$1.5 \mathrm{m} \mathrm{s}^{-1}$

Answer

$2.0 \mathrm{m} \mathrm{s}^{-1}$

Question 3

As shown in the figure, a bob of mass $m$ is tied to a massless string whose other end portion is wound on a flywheel (disc) of radius $r$ and mass $m$. When released from rest, the bob starts falling vertically. When it has covered a distance of $h$, the angular speed of the wheel will be:

Accepted Answer

$\frac{1}{r} \sqrt{\frac{4gh}{3}}$

Answer

$ r \sqrt{\frac{3}{2gh}} $

Answer

$\frac{1}{r} \sqrt{\frac{2gh}{3}}$

Answer

$ r \sqrt{\frac{3}{4gh}} $

Question 4

Which of the following gives a reversible operation?

Accepted Answer

""

Answer

Answer

Answer

Question 5

Consider a circular coil of wire carrying constant current $I$, forming a magnetic dipole. The magnetic flux through an infinite plane that contains the circular coil and excluding the circular coil area is given by ${\varphi}_{i}$. The magnetic flux through the area of the circular coil is given by ${\varphi}_{0}$. Which of the following options is correct?

Accepted Answer

$ \varphi_{i} = -\varphi_{0} $

Answer

$\varphi_{i} = \varphi_{0}$

Answer

$ {\varphi }_{i} > {\varphi }_{0} $

Answer

$ {\varphi }_{i} < {\varphi }_{0} $