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

The vector sum of a system of non-collinear forces acting on a rigid body is given to be non-zero. If the vector sum of all the torques due to the system of forces about a certain point is found to be zero, does this mean that it is necessarily zero about any arbitrary point?

For an ideal liquid ______.

1. the bulk modulus is infinite.
2. the bulk modulus is zero. 
3. the shear modulus is infinite.
4. the shear modulus is zero.

For an ideal liquid ______.

1. the bulk modulus is infinite.
2. the bulk modulus is zero. 
3. the shear modulus is infinite.
4. the shear modulus is zero.

What is the Bulk modulus for a perfect rigid body?

To what depth must a rubber ball be taken in deep sea so that its volume is decreased by 0.1%. (The bulk modulus of rubber is 9.8 × 10⁸ Nm^–2; and the density of sea water is 10³ kg m^–3.)

With increase in temperature, the viscosity of ______.

1. gases decreases.
2. liquids increases.
3. gases increases.
4. liquids decreases.

Is viscosity a vector?

Heat is associated with ______.

These days people use steel utensils with copper bottom. This is supposed to be good for uniform heating of food. Explain this effect using the fact that copper is the better conductor.

We would like to prepare a scale whose length does not change with temperature. It is proposed to prepare a unit scale of this type whose length remains, say 10 cm. We can use a bimetallic strip made of brass and iron each of different length whose length (both components) would change in such a way that difference between their lengths remain constant. If α_iron = 1.2 × 10⁻⁵/K and α_brass = 1.8 × 10⁻⁵/K, what should we take as length of each strip?

A thin rod having length L₀ at 0°C and coefficient of linear expansion α has its two ends maintained at temperatures θ₁ and θ₂, respectively. Find its new length.

According to Stefan’s law of radiation, a black body radiates energy σT⁴ from its unit surface area every second where T is the surface temperature of the black body and σ = 5.67 × 10^–8 W/m²K⁴ is known as Stefan’s constant. A nuclear weapon may be thought of as a ball of radius 0.5 m. When detonated, it reaches temperature of 106 K and can be treated as a black body.

1. Estimate the power it radiates.
2. If surrounding has water at 30°C, how much water can 10% of the energy produced evaporate in 1s?  [S_w = 4186.0 J/kg K and L_v = 22.6 × 10⁵ J/kg]
3. If all this energy U is in the form of radiation, corresponding momentum is p = U/c. How much momentum per unit time does it impart on unit area at a distance of 1 km?

What is the ratio between the distance travelled by the oscillator in one time period and amplitude?

A body of mass m is attached to one end of a massless spring which is suspended vertically from a fixed point. The mass is held in hand so that the spring is neither stretched nor compressed. Suddenly the support of the hand is removed. The lowest position attained by the mass during oscillation is 4 cm below the point, where it was held in hand.

Find the frequency of oscillation?

A train whistling at constant frequency is moving towards a station at a constant speed V. The train goes past a stationary observer on the station. The frequency n ′ of the sound as heard by the observer is plotted as a function of time t (figure). Identify the expected curve.

A train, standing in a station yard, blows a whistle of frequency 400 Hz in still air. The wind starts blowing in the direction from the yard to the station with a speed of 10 m/s. Given that the speed of sound in still air is 340 m/s ______.

1. the frequency of sound as heard by an observer standing on the platform is 400 Hz.
2. the speed of sound for the observer standing on the platform is 350 m/s.
3. the frequency of sound as heard by the observer standing on the platform will increase.
4. the frequency of sound as heard by the observer standing on the platform will decrease.

A sitar wire is replaced by another wire of same length and material but of three times the earlier radius. If the tension in the wire remains the same, by what factor will the frequency change?

A train standing at the outer signal of a railway station blows a whistle of frequency 400 Hz still air. The train begins to move with a speed of 10 ms^–1 towards the platform. What is the frequency of the sound for an observer standing on the platform? (sound velocity in air = 330 ms^–1)

A calorie is a unit of heat or energy and it equals about 4.2 J where 1J = 1 kg m²s^–2. Suppose we employ a system of units in which the unit of mass equals α kg, the unit of length equals β m, the unit of time is γ s. Show that a calorie has a magnitude 4.2 α^–1 β^–2 γ² in terms of the new units.

A book with many printing errors contains four different formulas for the displacement y of a particle undergoing a certain periodic motion:

(a) y = a sin `(2pit)/T`

(b) y = a sin vt

(c) y = `(a/T) sin  t/a`

d) y = `(a/sqrt2) (sin 2πt / T + cos 2πt / T )`

(a = maximum displacement of the particle, v = speed of the particle. T = time-period of motion). Rule out the wrong formulas on dimensional grounds.