Practice Questions, Science
Q1. Write the value of G in S.I. unit.Q2.What will be the value of g at centre of the Earth?
Q3.State Newton's universal law of gravitation.
Q4.Write the differences between g and G.
Q5.Write the differences between mass and weight.
Q6.Write the differences between distance and displacement.
Q7.Write the differences between speed and velocity.
Q8.Define acceleration.
Q9.State Newton's first law of motion.
Q10.State Newton's second law of motion .
GRAVITATION
Q11. What are fluids?Ans :Fluids are the substances that flow and lack a fixed shape, exert pressure in all directions and this pressure depends on the height of the fluid column above.
Q12. What is buoyant force ?
Ans: The upward force employed by a fluid which makes objects appear lighter when submerged, is called the buoyant force.
According to Archimedes' principle, the buoyant force equals the weight of the displaced fluid.
Q13. State Archimedes' principle.
Ans: Archimedes' principle states that whenever an object is immersed in a liquid (fully or partially), the liquid exerts on upward force upon the object.The amount of that force is equivalent to the weight of the liquid displaced by the object.
Q14. Write the applications of Archimedes principle.
Ans: (a) In evaluating relative density
(b) In designing ships and submarines.
(c) In making lactometers and hydrometers.
Q15. What is density?
Ans: Mass per unit volume of an object is called its density.
Density = Mass/volume
Q16. What is the S.I. unit of density?
Ans: kg/m3
Q17. What is relative density ?
Ans: The ratio of density of a substance to the density of water is called relative density of the object.
Relative density = (density of substance)/(density of water)
Q18. What is the S.I. unit of relative density?
Ans : Relative density has no unit. It is a pure number.
Q19. Why is water chosen as a reference?
Ans: Water is present everywhere on the Earth so it becomes easier to evaluate the density of a substance in relation to water.
Q20. When an object sinks or floats in water?
Ans: If relative density of an object is greater than 1, it sinks in water.
If relative density of an object is less than 1 , it floats on water.
WORK AND ENERGY
- When do we say that work is done?
Ans : Work is said to be done when -
(i) a force acts on an object, and
(ii) the object is displaced. - Write an expression for the work done when a force is acting on an object in the direction of its displacement.
Ans: Work done = force x Displacement
or,
W = F × S - Work done is scalar or vector?
Ans: Scalar - What is the S.I. unit of work done?
Ans: joule(J) - What is the C.G.S.. unit of work done?
Ans: erg - Define 1 J of work.
Ans: When a force of 1N causes a displacement of 1m in its own direction, then work done is said to be one joule.
i.e., 1J = 1N × 1m = 1Nm - Define 1 erg of work.
Ans: When a force of 1dyne causes a displacement of 1cm in its own direction, then work done is said to be one erg.
i.e., 1erg = 1dyn × 1cm = 1dyn-cm - At what conditions work done can be zero?
Ans: Work done is assumed zero when -
(i)no force is applied.
(ii) no displacement occurs.
(iii)applied force and displacement be perpendicular to each other. - A pair of bullocks exerts a force of 140 N on a plough. The field being ploughed is 15 m long. How much work is done in ploughing the length of the field?
Ans: Work done = F× s = 140 × 15 = 2100J - What is energy?
Ans: The capacity of doing work is called energy. - What is mechanical energy?
Ans: The energy stored to an object due to its motion or position is termed as mechanical energy. - What are the different types of mechanical energy?
Ans: Two types of mechanical energy are -
(i) Potential energy
(ii) Kinetic energy - What is the kinetic energy of an object?
Ans: The energy possessed by a body by virtue of its motion is called kinetic energy. - Write an expression for the kinetic energy of an object.
Ans: Kinetic energy, Ek = 1/2 m v2
where, m = mass of the object
v = speed of the object - Can kinetic energy be negative?
Ans: No kinetic energy can't be negative. It is always positive. - If velocity of an object be doubled , how many times will be the kinetic energy?
Ans: 4 times - If velocity of an object be halved , how many times will be the kinetic energy?
Ans: 1/4 times - If velocity of an object be doubled and its mass is done 4 times, how many times will be the kinetic energy?
Ans: ...... - certain force acting on a 20 kg mass changes its velocity from 5 m/s to 2 m/s. Calculate the work done by the force.
Ans: ...... - When will be the work done negative?
Ans: ...... - Define average power.
Ans : When a machine or person does different amounts of work or uses energy in different interval of time , the ratio between the total work or energy consumed to the total time is average power. - A lamp consumes 1000J of electrical energy in 10s. What is its power ?
Ans :- Power = W/t = 1000J / 10S = 100J/s = 100W. - A battery lights a bulb. Describe the energy change involved in the process.
Ans :- A battery changes chemical energy into electrical energy. When current passes through filament , first electrical energy converts into heat energy and then into light energy . - A mass of 10 kg is at a point A on the table. It is moved to a point B. If the line joining A and B is horizontal , what is the work done on the objects by the gravitational force ? Explain your answer.
Ans :- The work done is zero. This is because the gravitational force and displacement are perpendicular to each other. - The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
Ans :-It does not violate the law of conservation of energy. Whatever, the decrease in potential energy due to the loss of height , same is the increase in the kinetic energy due to increase in velocity of the body. - What are the various energy transformations that occur when you are riding a bicycle?
Ans :- The chemical energy of the food changes into heat and then to muscular energy . On paddling, the muscular energy changes into the mechanical energy. - Does the transfer of energy take place when you push a huge rock with all your might and fail to move it ? Where is the energy you spend going ?
Ans :- Energy transfer does not take place as no displacement takes place in the direction of applied force.The energy spent is used to overcome inertia of rest of the rock.
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