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Which of the following are chemical changes? (i) Decaying of wood (ii) Burning of wood (iii) Sawing of wood (iv) Hammering of a nail into a piece of wood (a) (i) and (ii) (b) (ii) and (iii) (c) (iii) and (iv) (d) (i) and (iv)

Answer: (a) (i) and (ii) Decaying of wood and burning of wood, because there will be a change of chemical composition and wood cannot be restored... View Article

Which of the following are physical changes? (i) Melting of iron metal (ii) Rusting of iron (iii) Bending of an iron rod (iv) Drawing a wire of iron metal (a) (i), (ii) and (iii) (b) (i), (ii) and (iv) (c) (i), (iii) and (iv) (d) (ii), (iii) and (iv)

Answer: (c) (i), (iii) and (iv) Rusting of iron is a chemical process where iron reacts with water and oxygen to produce iron oxide whereas other... View Article

Tincture of iodine has antiseptic properties. This solution is made by dissolving (a) iodine in potassium iodide (b) iodine in vaseline (c) iodine in water (d) iodine in alcohol

Answer: (d) iodine in alcohol In the tincture of iodine, the solvent is alcohol and water while the solute is iodine. A tincture of iodine is... View Article

A mixture of sulphur and carbon disulphide is (a) heterogeneous and shows Tyndall effect (b) homogeneous and shows Tyndall effect (c) heterogeneous and does not show Tyndall effect (d) homogeneous and does not show Tyndall effect

Answer: (a) heterogeneous and shows Tyndall effect A mixture of sulphur and carbon disulphide is a heterogeneous colloid and shows the Tyndall... View Article

Rusting of an article made up of iron is called (a) corrosion and it is a physical as well as chemical change (b) dissolution and it is a physical change (c) corrosion and it is a chemical change d) dissolution and it is a chemical change

Answer: (c) corrosion and it is a chemical change Rusting of iron is corrosion and it’s a chemical change because rust is a chemical... View Article

Which of the following statements are true for pure substances? (i) Pure substances contain only one kind of particles (ii) Pure substances may be compounds or mixtures (iii) Pure substances have the same composition throughout (iv) Pure substances can be exemplified by all elements other than nickel (a) (i) and (ii) (b) (i) and (iii) (c) (iii) and (iv) (d) (ii) and (iii)

Answer: (b) (i) and (iii) Pure substances are substances that are made up of only one kind of particle and have a fixed or constant structure.... View Article

Compare the power at which each of the following is moving upwards against the force of gravity? (given g = 10 m s–2) (i) a butterfly of mass 1.0 g that flies upward at a rate of 0.5 m s–1. (ii) a 250 g squirrel climbing up on a tree at a rate of 0.5 m s–1.

Answer: (i) a butterfly of mass 1.0 g that flies upward at a rate of 0.5 m s-1. Mass of butterfly (mb) = 1 g = 10-3 kg Speed (vb) = 0.5 ms-1... View Article

Define watt. Express kilowatt in terms of joule per second. A 150 kg car engine develops 500 W for each kg. What force does it exert in moving the car at a speed of 20 m s–1?

Answer: Power is defined as the rate at which work is done upon an object. Power is a time-based quantity. Which is related to how fast a job is... View Article

How is the power related to the speed at which a body can be lifted? How many kilograms will a man working at the power of 100 W, be able to lift at a constant speed of 1 m s –1 vertically? (g = 10 m s–2)

Answer: Power is defined as the rate at which work is done upon an object. Power is a time-based quantity. Which is related to how fast a job is... View Article

What is power? How do you differentiate kilowatt from kilowatt-hour? The Jog Falls in Karnataka state are nearly 20 m high. 2000 tonnes of waterfalls from it in a minute. Calculate the equivalent power if all this energy can be utilized? (g = 10 m s–2)

Answer: Power is defined as the rate at which work is done upon an object. Power is a time-based quantity. Which is related to how fast a job is... View Article

Four men lift a 250 kg box to a height of 1 m and hold it without raising or lowering it. (a) How much work is done by the men in lifting the box? (b) How much work do they do in just holding it? (c) Why do they get tired while holding it? (g = 10 m s–2)

Answer: Given m = 250kg Height (h) = 1 m Acceleration due to gravity g = 10 ms-2 (a) Work done by the men in lifting the box = F × s Work... View Article

A girl having a mass of 35 kg sits on a trolley of mass 5 kg. The trolley is given an initial velocity of 4 m s–1 by applying a force. The trolley comes to rest after traversing a distance of 16 m. (a) How much work is done on the trolley? (b) How much work is done by the girl?

Answer: Initial velocity of the trolley (u) = 4 m/s Final velocity of the trolley (v) = 0 Mass of the trolley (m) = 5 kg Distance covered by the... View Article

An automobile engine propels a 1000 kg car (A) along a levelled road at a speed of 36 km h–1. Find the power if the opposing frictional force is 100 N. Now, suppose after travelling a distance of 200 m, this car collides with another stationary car (B) of same mass and comes to rest. Let its engine also stop at the same time. Now car (B) starts moving on the same level road without getting its engine started. Find the speed of the car (B) just after the collision.

Answer: Mass of the car A (mA) = 1000 kg Initial speed of the car A, uA = 36 kmh-1 uA = 36 x (5/18) uA = 10m s-1 m(A)= m(B) = 1000 kg. Frictional... View Article

A light and a heavy object have the same momentum. Find out the ratio of their kinetic energies. Which one has a larger kinetic energy?

Answer: Let m be the mass and v is the velocity of the light object. M be the mass and V is the velocity of the heavy object. Since both have the... View Article

If an electric iron of 1200 W is used for 30 minutes everyday, find electric energy consumed in the month of April.

Answer: 18units Power of electric iron (P) = 1200W Usage per day = 30min =30/60hrs =0.5hrs Number of days in the month of April=30days The... View Article

Is it possible that an object is in the state of accelerated motion due to external force acting on it, but no work is being done by the force? Explain it with an example.

Answer: Yes, an object can be in a state of accelerated motion due to an external force acting on it, but no work is being done by the force.... View Article

The velocity of a body moving in a straight line is increased by applying a constant force F, for some distance in the direction of the motion. Prove that the increase in the kinetic energy of the body is equal to the work done by the force on the body.

Answer: We know that v2- u2 = 2as s = v2 - u2/2a F = m × a W = ma(v2 - u2)/2a W = 1/2 mv2 - 1/2 mu2 W = (K.E)f - (K.E)i W = Final kinetic... View Article

The weight of a person on a planet A is about half that on the earth. He can jump upto 0.4 m height on the surface of the earth. How high he can jump on the planet A?

Answer: Person on planet A can jump a height of 0.8 m because the weight of the person on plat A is half the weight that of earth. Hence... View Article

Can any object have momentum even if its mechanical energy is zero? Explain.

Answer: No, Because its potential and kinetic energy are zero. Mechanical energy = kinetic energy + potential energy Mechanical energy = 0 Since... View Article

Can any object have mechanical energy even if its momentum is zero? Explain.

Answer: Momentum is how we measure mass that is in motion. Any moving object will have momentum. Under the law of physics, the object’s... View Article

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