Model Test Paper മാതൃകാ ചോദ്യപേപ്പർ
A full paper in the Kerala Class 9 Physics pattern for this chapter, covering the whole of “Buoyant Force” – measuring the buoyant force, the factors that decide it, Archimedes’ principle, the principle of floatation, relative density, the hydrometer and lactometer, and their uses. Several questions are numericals that switch between kgwt and newton. Work on paper with a timer before you look at the solutions.
Standard IX · Physics
Chapter 5 · പ്ലവക്ഷമബലം · Buoyant Force
- The first 15 minutes are cool-off time: read every question and plan your answers; do not write.
- Answer all questions. Marks for each question are shown on the right.
- For numericals write Given → Formula → Substitution → Answer with the unit. Take g = 9.8 m/s2, 1 kgwt = 9.8 N and the density of water = 1000 kg/m3.
- Relative density has no unit.
SECTION AAnswer all · 8 × 1 = 8 marks
1.
Liquids and gases together are called .
(1)2.
An object weighs 12 N in air and 9 N when it is fully immersed in water. The buoyant force on it is
(1)(a) 21 N(b) 12 N(c) 9 N(d) 3 N
3.
The unit of relative density is
(1)(a) kg/m3(b) g/cm3(c) N(d) it has no unit
4.
Find the relation and fill in: hydrometer : relative density of liquids :: lactometer :
(1)5.
A wooden block floats in water. The buoyant force on it is
(1)(a) greater than its weight(b) less than its weight(c) equal to its weight(d) zero
6.
A 100 g brass weight is fully immersed in turn in each liquid below. In which is the buoyant force on it the greatest?
(1)(a) kerosene(b) water(c) saturated salt solution(d) glycerine
7.
The density of mercury is 13 600 kg/m3. Its relative density is .
(1)8.
The scientist of Syracuse who found the volume of the king’s crown from the water that overflowed when he got into a full bathtub was .
(1)SECTION BAnswer all · 5 × 2 = 10 marks
9.
An object weighs 0.6 kgwt in air and 0.45 kgwt when it is fully immersed in water. (a) Find the buoyant force on it in kgwt. (b) Express it in newton. (1 kgwt = 9.8 N)
(2)10.
A ship rises a little out of the water when it sails from a river into the sea. Why?
(2)11.
A small iron nail sinks in water, but a huge ship made of iron floats. Explain.
(2)12.
The density of coconut oil is 920 kg/m3. (a) Find its relative density. (b) Will coconut oil float on water? Why?
(2)13.
A lactometer is placed first in pure milk and then in milk to which water has been added. (a) In which does it sink deeper? (b) Why?
(2)SECTION CAnswer all · 4 × 3 = 12 marks
14.
A stone of mass 0.5 kg weighs 4.9 N in air. When fully immersed in water, the spring balance reads 3.9 N (figure). (a) Find the buoyant force. (b) Find the volume of the stone. (c) What will the balance read if the stone is fully immersed in saturated salt solution (density 1025 kg/m3)? (g = 9.8 m/s2, density of water 1000 kg/m3)
(3)15.
A 100 g brass weight (weight in air 0.98 N) is fully immersed in three liquids P, Q and R. The spring balance readings are shown below.
(a) Find the buoyant force in each liquid. (b) Which liquid is the densest? Why? (c) Q is glycerine and R is water. Is P kerosene or saturated salt solution? Give a reason.
(3)| Liquid | P | Q | R |
|---|---|---|---|
| Reading (N) | 0.881 | 0.826 | 0.858 |
16.
A wooden block of mass 0.6 kg floats in water. (a) What is its weight in newton? (b) What is the buoyant force on it? (c) Find the volume of water it displaces. (g = 9.8 m/s2, density of water 1000 kg/m3)
(3)17.
A crown said to be made of pure gold has a mass of 1 kg. When it is lowered into a jar full of water, 60 cm3 of water overflows. (Density of pure gold = 19 300 kg/m3.) (a) What is the volume of the crown? Why? (b) Find the density of the crown. (c) Is the crown pure gold? Explain.
(3)SECTION DAnswer all · 2 × 5 = 10 marks
18.
A hydrometer floats in water and in a liquid X as shown in the figure. (a) What is a hydrometer? On what principle does it work? (b) What does it read in pure water? (c) In X it floats higher than in water. Is the relative density of X more or less than 1? (d) The density of kerosene is 810 kg/m3. Find its relative density, and say whether the hydrometer will float higher or sink deeper in kerosene than in water. (e) Why do the values on a hydrometer scale increase downwards?
(5)19.
A house boat on Vembanad lake displaces 3000 kg of water. (a) Find the buoyant force on it in kgwt and in newton. (b) What is the weight of the boat? Which principle tells you this? (c) Four tourists of total mass 240 kg get on. How much more water does the boat displace? Give the mass and the volume. (d) Life jackets are compulsory on such boats. Explain why, using the idea of buoyant force.
(5)