Science (English Medium) कक्षा ११ - CBSE Question Bank Solutions for Physics

Equation of a plane progressive wave is given by `y = 0.6 sin 2π (t - x/2)`. On reflection from a denser medium its amplitude becomes 2/3 of the amplitude of the incident wave. The equation of the reflected wave is ______.

During propagation of a plane progressive mechanical wave ______.

1. all the particles are vibrating in the same phase.
2. amplitude of all the particles is equal.
3. particles of the medium executes S.H.M.
4. wave velocity depends upon the nature of the medium.

The speed-time graph of a particle moving along a fixed direction is shown in Fig. 3.28. Obtain the distance traversed by the particle between (a) t = 0 s to 10 s, (b) t = 2 s to 6 s.

What is the average speed of the particle over the intervals in (a) and (b)

The velocity-time graph of a particle in one-dimensional motion is shown in Figure

Which of the following formulae are correct for describing the motion of the particle over the time-interval t₂ to t₁?

(a) x(t₂) = x(t₁) + v(t₁)(t₂–t₁) + (1/2)a(t₂–t₁)²

(b) v(t₂)= v(t₁) + a(t₂–t₁)

(c) v_Average = (x(t₂) – x(t₁)) / (t₂ – t₁)

(d) a_Average = (v(t₂) – v(t₁)) / (t₂ – t₁)

(e) x(t₂) = x(t₁) + v_Average(t₂ – t₁) + (1/2)a_Average(t₂ – t₁)²

(f) x(t₂) – x(t₁) = area under the v–t curve bounded by the t-axis and the dotted line shown.

Choose the correct alternative:

If the zero of potential energy is at infinity, the total energy of an orbiting satellite is negative of its kinetic/potential energy.

Choose the correct alternative:

The energy required to launch an orbiting satellite out of earth’s gravitational influence is more/less than the energy required to project a stationary object at the same height (as the satellite) out of earth’s influence.

A satellite orbits the earth at a height of 400 km above the surface. How much energy must be expended to rocket the satellite out of the earth’s gravitational influence? Mass of the satellite = 200 kg; mass of the earth = 6.0 ×10²⁴ kg; radius of the earth = 6.4 ×10⁶ m; G = 6.67 × 10^–11 N m² kg^–2

A body is moving unidirectionally under the influence of a source of constant power. Its displacement in time t is proportional to ______.

A pump on the ground floor of a building can pump up water to fill a tank of volume 30 m³ in 15 min. If the tank is 40 m above the ground, and the efficiency of the pump is 30%, how much electric power is consumed by the pump?

The blades of a windmill sweep out a circle of area A.

1. If the wind flows at a velocity v perpendicular to the circle, what is the mass of the air passing through it in time t?
2. What is the kinetic energy of the air?
3. Assume that the windmill converts 25% of the wind’s energy into electrical energy, and that A = 30 m², v = 36 km/h and the density of air is 1.2 kg m^–3. What is the electrical power produced?

A family uses 8 kW of power.

1. Direct solar energy is incident on the horizontal surface at an average rate of 200 W per square meter. If 20% of this energy can be converted to useful electrical energy, how large an area is needed to supply 8 kW?
2. Compare this area to that of the roof of a typical house.

Prove the theorem of perpendicular axes.

(Hint: Square of the distance of a point (x, y) in the x–y plane from an axis through the origin perpendicular to the plane is x² + y²).

Prove the theorem of parallel axes.

(Hint: If the centre of mass is chosen to be the origin `summ_ir_i = 0`

Explain why The angle of contact of mercury with glass is obtuse, while that of water with glass is acute

Explain why Water on a clean glass surface tends to spread out while mercury on the same surface tends to form drops. (Put differently, water wets glass while mercury does not.)

Explain why Surface tension of a liquid is independent of the area of the surface

Explain why Water with detergent dissolved in it should have small angles of contact.

Explain why A drop of liquid under no external forces is always spherical in shape

Fill in the blanks using the word(s) from the list appended with each statement

Surface tension of liquids generally . . . with temperatures (increases / decreases)

A U-shaped wire is dipped in a soap solution and removed. The thin soap film formed between the wire and the light slider supports a weight of 1.5 × 10^–2 N (which includes the small weight of the slider). The length of the slider is 30 cm. What is the surface tension of the film?