Q. A force is applied on a body of mass $20kg$ moving with a velocity of $40m{s}^{-1}$. The body attains a velocity of $50m{s}^{-1}$ in $2$ seconds. Calculate the work done to attain this velocity.

Q. (i) In what way does an 'Ideal machine' differ from a 'Practical machine'?
(ii) Can a single machine act as a force multiplier and a speed multiplier at the same time?

Q. (i) It is observed that the temperature of the surroundings starts falling when the ice in a frozen lake starts melting. Give a reason for the observation.
(ii) How is the heat capacity of the body related to its specific heat capacity?

Q. A girl of mass $35kg$ climbs up from the first floor of a building at a height $4m$ above the ground to the third floor at a height $12m$ above the ground. What will be the increase in her gravitational potential energy? $(g=10m{s}^{-2})$.

Q. Which of the radioactive radiations :
(i) Can cause severe genetical disorders.
(ii) Are deflected by an electric field?

Q. Calculate the equivalent resistance between the points $A$ and $B$ for the following combination of resistors:

Q. (i) Can the absolute refractive index of a medium be less than one?
(ii) A coin placed at the bottom of a beaker appears to be raised by $4.0cm$. If the refractive index of water is $4/3$, find the depth of the water in the beaker.

Q. A vibrating tuning fork is placed over the mouth of a burette, filled with water. The tap of the burette is opened and the water level gradually starts falling. It is found that the sound from the tuning fork becomes very loud for a particular length of the water column.
(i) Name the phenomenon taking place when this happens.
(ii) Why does the sound become very loud for this length of the water column?

Q. (i) What is the principle on which SONAR is based?
(ii) An observer stands at a certain distance away from a cliff and produces a loud sound. He hears the echo of the sound after $1.8s$. Calculate the distance between the cliff and the observer if the velocity of sound in air is $340m{s}^{-1}$.

Q. Give any two effects of a force on a non-rigid body.

Q. A radioactive nucleus undergoes a series of decays according to the sequence
$X\underrightarrow{\beta }{X}_1\underrightarrow{\alpha }{X}_2\underrightarrow{\alpha }{X}_3$
If the mass number and atomic number of $X_3$ are $172$ and $69$ respectively, what is the mass number and atomic number of $X$?

Q. A ray of light is moving from a rarer medium to a denser medium and strikes a plane mirror placed at ${90}^o$ to the direction of the ray as shown in the diagram.
(i) Copy the diagram and mark arrows to show the path of the ray of light after it is reflected from the mirror.
(ii) Name the principle you have used to mark the arrow to show the direction of the ray.

Q. Which class of lever found in the human body is being used by a boy :
(i) When he holds a load on the palm of his hand.
(ii) When he raises the weight of his body on his toes?

Q. (i) Where is the centre of gravity of a uniform ring situated?
(ii) "The position of the centre of gravity of a body remains unchanged even when the body is deformed". State whether this statement is true or false.

Q. A type of single pulley is very often used as a machine even though it does not give any gain in mechanical advantage.
(i) Name the type of pulley used.
(ii) For what purpose is such a pulley used?

Q. One end of a spring is kept fixed while the other end is stretched by a force as shown in the diagram.
(i) Copy the diagram and mark on it the direction of the restoring force.
(ii) Name one instrument which works on the above principle.

Q. A block and tackle system of pulleys has a velocity ratio $4$.
(i) Draw a labelled diagram of the system indicating clearly the points of application and direction of load and effort.
(ii) What is the value of the mechanical advantage of the given pulley system if it is an ideal pulley system?

Q. Define the term 'Heat capacity' and state its S.I. unit.

Q. You have been provided with a solenoid $AB$.
(i) What is the polarity at end $A$?
(ii) Give one advantage of an electromagnet over a permanent magnet.

Q. A sound made on the surface of a lake takes $3s$ to reach a boatman. How much time will it take to reach a diver inside the water at the same depth?
Velocity of sound in air $=330m{s}^{-1}$.
Velocity of sound in water $=1450m{s}^{-1}$.

Q. A bucket kept under a running tap is getting filled with water. A person sitting at a distance is able to get an idea when the bucket is about to be filled.
(i) What change takes place in the sound to give this idea?
(ii) What causes the change in the sound?

Q. (i) The refractive index of glass with respect to air is $1.5$. What is the value of the refractive index of air with respect to glass?
(ii) A ray of light is incident as a normal ray on the surface of separation of two different media. What is the value of the angle of incidence in this case?

Q. Name the radiations :
(i) That are used for photography at night.
(ii) Used for detection of fraction in bones.
(iii) Whose wavelength range is from $100\mathring{A}$ to $4000\mathring{A}$ (or $10nm$ to $400nm$).

Q. How much heat energy is released when $5g$ of water at ${20}^{o}C$ changes to ice at $0^{o}C$?
[Specific heat capacity of water $=4.2J{g}^{-1}{C}^{-1}$.
Specific latent heat of fusion of ice $=336J{g}^{-1}$]

Q. (i) With reference to their direction of action, how does a centripetal force differ from a centrifugal force?
(ii) State the Principle of conservation of energy.
(iii) Name the form of energy which a body may possess even when it is not in motion.

Q. An object $AB$ is placed between $2F_1$ and $F_1$ on the principal axis of a convex lens. Obtain the image of the object formed by the lens.

Q. (i) What is meant by the terms amplitude and frequency of a wave?
(ii) Explain why stringed musical instruments, like the guitar, are provided with a hollow box.

Q. A coolie is pushing a box weighing $1500N$ up an inclined plane $7.5m$ long on to a platform, $2.5m$ above the ground.
(i) Calculate the mechanical advantage of the inclined plane.
(ii) Calculate the effort applied by the coolie.
(ii) In actual practice, the coolie needs to apply more effort than what is calculated. Give one reason why you think the coolie needs to apply more effort.

Q. (i) Name the device used to protect the electric circuits from overloading and short circuits.
(ii) On what effect of electricity does the above device work?

Q. What is meant by Global warming?