Practice problems on JEE Mains, JEE Mains 2021 Aug 26 Shift 2

Question 1

The temperature of equal masses of three different liquids x, y and z are 10ºC, 20ºC and 30ºC respectively. The temperature of mixture when x is mixed with y is 16°C and that when y is mixed with z is 26ºC. The temperature of mixture when x and z are mixed will be :

Accepted Answer

23.84ºC

Answer

20.28ºC

Answer

25.62ºC

Answer

28.32ºC

Question 2

Two blocks of masses 3 kg are connected by a metal wire going over a smooth pulley. The breaking stress of the metal is π24​×102Nm−2. What is the minimum radius of the wire ? (take g = 10 ms−2)

Accepted Answer

12.5 cm

Answer

1250 cm

Answer

1.25 cm

Answer

125 cm

Question 3

The locus of the mid points of the chords of the hyperbola x2−y2=4, which touch the parabola y2=8x, is:

Accepted Answer

y2(x−2)=x3

Answer

x3(x−2)=y2

Answer

y3(x−2)=x2

Answer

x2(x−2)=y3

Question 4

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).Assertion (A) : Heavy water is used for the study of reaction mechanism.Reason (R) : The rate of reaction for the cleavage of O-H bonds is slower than that of O–D bond.Choose the most appropriate answer from the options given below:

Accepted Answer

(A) is true but (R) is false

Answer

Both (A) and (R) are true but (R) is not the true explanation of (A)

Answer

(A) is false but (R) is true

Answer

Both (A) and (R) are true and (R) is the true explanation of (A)

Question 5

Given below are two statements:Statements I : Sphalerite is a sulphide ore of zinc and copper glance is a sulphide ore of copper.Statements II: It is possible to separate two sulphide ores by adjusting proportion of oil to water or by using 'depressants' in a froth flotation method.Choose the most appropriate answer from the options given below:

Accepted Answer

Both Statement I and Statement II are true

Answer

Statement I is true but Statement II is false

Answer

Statement I is false but Statement II is true

Answer

Both Statement I and Statement II are false

Question 6

An electric bulb of 500 watt at 100 volt is used in a circuit having a 200 V supply. Calculate the resistance R to be connected in series with the bulb so that the power delivered by the bulb is 500 W.

Accepted Answer

20 Ω

Answer

10 Ω

Answer

5 Ω

Answer

30 Ω

Question 7

A transmitting antenna at top of a tower has a height of 50 m and the height of receiving antenna is80 m. What is the range of communication for Line of Sight (LoS) mode ?[use radius of earth = 6400 km]

Accepted Answer

57.28 km

Answer

80.2 km

Answer

144.1 km

Answer

45.5 km

Question 8

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).Assertion (A) : Photochemical smog causes cracking of rubber.Reason (R) : Presence of ozone, nitric oxide, acrolein, formaldehyde and peroxyacetyl nitrate in photochemical smog makes it oxidizing.Choose the most appropriate answer from the options given below:

Accepted Answer

Both (A) and (R) are true and (R) is the true explanation of (A)

Answer

(A) is false but (R) is true

Answer

Both (A) and (R) are true but (R) is not the true explanation of (A)

Answer

(A) is true but (R) is false

Question 9

Chalcogen group elements are:

Accepted Answer

Se, Te and Po

Answer

O, Ti and Po

Answer

Se, Tb and Pu

Answer

S, Te and Pm

Question 10

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).Assertion (A) : Sucrose is a disaccharide and a non-reducing sugar.Reason (R) : Sucrose involves glycosidic linkage between C1​ of β-glucose and C2​ of α -fructose.Choose the most appropriate answer from the options given below:

Accepted Answer

(A) is true but (R) is false

Answer

Both (A) and (R) are true but (R) is not the true explanation of (A)

Answer

(A) is false but (R) is true

Answer

Both (A) and (R) are true and (R) is the true explanation of (A)

Question 11

The interaction energy of London forces between two particles is proportional to rx, where r is the distance between the particles. The value of x is:

Accepted Answer

–6

Answer

6

Answer

–3

Answer

3

Question 12

A bomb is dropped by a fighter plane flying horizontally. To an observer sitting in the plane, the trajectory of the bomb is a :

Accepted Answer

Straight line vertically down the plane

Answer

Hyperbola

Answer

Parabola in a direction opposite to the motion of plane

Answer

Parabola in the direction of motion of plane

Question 13

A cylindrical container of volume 4.0×10−3 m3 contains one mole of hydrogen and two moles of carbon dioxide. Assume the temperature of the mixture is 400 K. The pressure of the mixture of gases is: (Take gas constant as 8.3 J mol−1 K−1)

Accepted Answer

24.9×105 Pa

Answer

249×101 Pa

Answer

24.9 Pa

Answer

24.9×103 Pa