A block of wood of volume 25 cm3 floats in water with 20 cm3 of its volume immersed. Calculate:
i) the density, andii) the weight of the block of wood.
Total volume of wood = 25 cm3
Volume of wood immersed = 20 cm3
Volume of wood outside water = 25 – 20 = 5 cm3.
ii) Weight of the block of wood = Volume of wood x density of wood
= 25 x 0.8
= 20 gf
Mention two properties of a wave: one property which varies and the other which remains constant when the wave passes from one medium to another.
The two properties are:
i) Wavelength ii) Frequency
The work done by the heart is 1 Joule per beat. Calculate the power of the heart if it beats 72 times in one minute.
Work done in one beat = 1 J
Work done in 72 beats = 1 x 72 = 72 J = 60 sec
Therefore, power = P = W/t = 72 / 60 = 1.2 W
State two advantages of an aneroid barometer.
i) It has no liquid, hence it is portable and quite easy to use.
ii) It has a caliberated scale from which the value of pressure can be read differently.
State Newton’s Second Law of motion.
Newton’s second law of motion states that the rate of change of linear momentum is directly proportional to the applied force and takes place in the direction of the applied force.
Which physical quantity does this electronvolt measure? How is it related to the S.I. unit of this quantity?
Electronvolt measures energy.
It is related to the S.I. unit of enrgy joule as 1 eV = 1.6 x 10-19 J.
Explain briefly what causes the twinkling of stars at night?
What should be the angle between force and displacement be to get the
i) minimum workii) maximum work?
i) For minimum work to be done, the angle should be 90o
ii) For maximum work, the angle should be 0o.
What is meant by the statement, ‘ the critical angle for diamond is 24o? How is the critical angle of a material related to its refractive index?
Critical angle of diamond is 24o means that the angle of incidence of light in diamond is such that the angle of refraction for it in air is 90o.The critical angle is related to the refractive index of the material as,
Explain why a gas bubble released at the bottom of a lake grows in size as it rises to the surface of the lake?
When the gas bubble, is at the bottom of the lake, it is under tremendous pressure of water. As the bubble begins to rise, the pressure of water on it begins to decrease. According to the Boyle’s law, volume is inversely proportional to pressure. Therefore, the volume of the bubble increases.