21.

When two springs A and B with force constants k_A and k_B are stretched by the same force, then the respective ratio of the work done on them is 

• k_B : k_A

• k_A : k_B

• k_A : k_B : 1

• $\sqrt{{\mathrm{k}}_{\mathrm{B}}} : \sqrt{{\mathrm{k}}_{\mathrm{A}}}$

For a particle moving according to the equation $\mathrm{x} = \mathrm{a} \cos \mathrm{\pi } \mathrm{t},$ the displacement in 3 s is

• 0

• 0.5 a

• 1.5 a

• 2 a

Two capillary tubes A and B of diameter 1 mm and 2 mm respectively are dipped vertically in a liquid. If the capillary rise in A is 6 cm, then the capillary rise in B is

• 2 cm

• 3 cm

• 4 cm

• 6 cm

Two wires A and B of same material and of equal length with the radii in the ratio 1 : 2 are subjected to identical loads. If the lengthof A increases by 8 mm, then the  increase in length of B is

• 2 mm

• 4 mm

• 8 mm

• 16 mm

After terminal velocity is reached, the acceleration of a body falling through a fluid is

• equal to g

• zero

• less than g

• greater than g

A liquid is filled upto a height of 20 min a cylindrical vessel. The speed of liquid coming out of a small hole at the bottom of the vessel is (take, g = 10ms^-2)

• 1.2 ms^-1

• 1 ms^-1

• 2 ms^-1

• 3.2 ms^-1

A metallic bar of coefficient of linear expansion 10^-5 K^-1 is heated from 0°C to 100°C. The percentage increase in its length is

• 0.1 % 

• 1 % 

• 10 %

• 0.01 %

Two perfectly black spheres A and B having radii 8 cm and 2 cm are maintained at temperatures 127°C and 527°C, respectively. The ratio of the energy radiated by A to that by B is

• 1 : 2

• 1 : 1

• 2 : 1

• 1 : 4

For a monoatomic gas, the molar specific heat at constant pressure divided by the molar gas constant R is equal to

• 2.5

• 1.5

• 5.0

• 3.5

Hot water in a vessel kept in a room cools from 70°C to 65°C in t₁ minutes, from 65°C to 60°C in t₂ minutes and from 60°C to 55°C in t₃ minutes then,

• t₁ < t₂ > t₃

• t₁ = t₂ = t₃

• t₁ < t₂ < t₃

• t₁ < t₂ = t₃