List of top Physics Questions asked in CBSE Class XI

A simple pendulum of length l with a bob of mass M is suspended in a car. The car is moving on a circular track of radius R with a uniform speed v. If the pendulum makes small oscillations in a radial direction about its equilibrium position, what will be its time period?

The piston in the cylinder head of a locomotive has a stroke (twice the amplitude) of 1.0 m. If the piston moves with simple harmonic motion with an angular frequency of 200 rad/min, what is its maximum speed?

A steel wire of length 4.7 m and cross-sectional area 3.0 × 10-5 m2 stretches by the same amount as a copper wire of length 3.5 m and cross-sectional area of 4.0 × 10–5 m2 under a given load. What is the ratio of the Young’s modulus of steel to that of copper?

A body weighs 63 N on the surface of the earth. What is the gravitational force on it due to the earth at a height equal to half the radius of the earth ?
A Saturn year is 29.5 times the earth year. How far is the Saturn from the sun if the earth is 1.50×108 km away from the sun ?

Explain why (or how):
(a) in a sound wave, a displacement node is a pressure antinode and vice versa,
(b) bats can ascertain distances, directions, nature, and sizes of the obstacles
without any “eyes”,
(c) a violin note and sitar note may have the same frequency, yet we can
distinguish between the two notes,
(d) solids can support both longitudinal and transverse waves, but only
longitudinal waves can propagate in gases, and
(e) the shape of a pulse gets distorted during propagation in a dispersive medium.

Two sitar strings A and B playing the note ‘Ga’ are slightly out of tune and produce beats of frequency 6 Hz. The tension in the string A is slightly reduced and the beat frequency is found to reduce to 3 Hz. If the original frequency of A is 324 Hz, what is the frequency of B?

A steel rod 100 cm long is clamped at its middle. The fundamental frequency of longitudinal vibrations of the rod are given to be 2.53 kHz. What is the speed of sound in steel?

One end of a U-tube containing mercury is connected to a suction pump and the other end to atmosphere. A small pressure difference is maintained between the two columns. Show that, when the suction pump is removed, the column of mercury in the U-tube executes simple harmonic motion.

The acceleration due to gravity on the surface of moon is 1.7 ms-2.What is the time period of a simple pendulum on the surface of moon if its time period on the surface of earth is 3.5 s? (g on the surface of earth is 9.8 ms-2

Two wires of diameter 0.25 cm, one made of steel and the other made of brass are loaded as shown in Fig. 8.11. The unloaded length of steel wire is 1.5 m and that of brass wire is 1.0 m. Compute the elongations of the steel and the brass wires.

The unloaded length of steel wire

Read the following two statements below carefully and state, with reasons, if it is true or false. 

(a) The Young’s modulus of rubber is greater than that of steel; 

(b) The stretching of a coil is determined by its shear modulus.

The stress-strain graphs for materials A and B are shown in Fig. 8.10. 

The stress-strain graphs for materials

The graphs are drawn to the same scale. 

(a) Which of the materials has the greater Young’s modulus? 

(b) Which of the two is the stronger material?

How will you ‘weigh the sun’, that is estimate its mass? The mean orbital radius of the earth around the sun is 1.5×108 km.

A rocket is fired from the earth towards the sun. At what distance from the earth’s centre is the gravitational force on the rocket zero ? Mass of the sun = 2×1030 kg, mass of the earth = 6×1024 kg. Neglect the effect of other planets etc. (orbital radius= 1.5 × 1011 m).

A pipe 20 cm long is closed at one end. Which harmonic mode of the pipe is resonantly excited by a 430 Hz source ? Will the same source be in resonance with the pipe if both ends are open? (speed of sound in air is 340 m s-1).
A Cylindrical piece of cork of density of base area A and height h floats in a liquid of density \(\rho_l\) .The cork is depressed slightly and then released. Show that the cork oscillates up and down simple harmonically with a period
\(T\) = \(2π\sqrt{\frac{h\rho}{\rho_lg}}\)
Where \(\rho\) is the density of cork. (Ignore damping due to viscosity of the liquid).

From a uniform disk of radius R, a circular hole of radius \(\frac{R}{2}\) is cut out. The centre of the hole is at \(\frac{R}{2}\) from the centre of the original disc. Locate the centre of gravity of the resulting flat body.

To maintain a rotor at a uniform angular speed of 200 rad s-1, an engine needs to transmit a torque of 180 N m. What is the power required by the engine ? (Note: uniform angular velocity in the absence of friction implies zero torque. In practice, applied torque is needed to counter frictional torque). Assume that the engine is 100% efficient.

A solid cylinder of mass 20 kg rotates about its axis with angular speed 100 rad s-1. The radius of the cylinder is 0.25 m. What is the kinetic energy associated with the rotation of the cylinder? What is the magnitude of angular momentum of the cylinder about its axis?

Torques of equal magnitude are applied to a hollow cylinder and a solid sphere, both having the same mass and radius. The cylinder is free to rotate about its standard axis of symmetry, and the sphere is free to rotate about an axis passing through its centre. Which of the two will acquire a greater angular speed after a given time.
Figures 13.20 correspond to two circular motions. The radius of the circle, the period of revolution, the initial position, and the sense of revolution (i.e. clockwise or anti clockwise) are indicated on each figure.
two circular motions
Obtain the corresponding simple harmonic motions of the x-projection of the radius vector of the revolving particle P, in each case.
How much should the pressure on a litre of water be changed to compress it by 0.10%? carry one quarter of the load.
Determine the volume contraction of a solid copper cube, 10 cm on an edge, when subjected to a hydraulic pressure of 7.0 × 106 Pa.
Explain why
  1. a horse cannot pull a cart and run in empty space,
  2. passengers are thrown forward from their seats when a speeding bus stops suddenly,
  3. it is easier to pull a lawn mower than to push it,
  4. a cricketer moves his hands backwards while holding a catch.