ICSE Living Science Physics for Class 6 Solutions Chapter 5 Pressure

Check Your Progress (Page 55)

Fill in the blanks.

Question 1.
Smaller the area on which a force acts, ………….. is the effect of force.
Answer:
Smaller the area on which a force acts, greater is the effect of force.

Question 2.
Magnitude of force is also known as ……………
Answer:
Magnitude of force is also known as thrust.

Question 3.
Pressure exerted on a surface depends upon …………. and …………..
Answer:
Pressure exerted on a surface depends upon area in contact and magnitude of force applied.

Question 4.
The SI unit of pressure is …………….
Answer:
The SI unit of pressure is pascal (Pa).

Question 5.
If a force of 12 N acts on an area of 4 m2, then the pressure exerted on the surface is …………..
Answer:
If a force of 12 N acts on an area of 4 m2, then the pressure exerted on the surface is 3N/m2 or 3Pa.

Question 6.
If the thrust acting on a surface decreases, then the pressure will …………..
Answer:
If the thrust acting on a surface decreases, then the pressure will decrease.

A. Tick the most appropriate answer.

Question 1.
Pressure is defined as –
a. force + area
b. force x area
c. force -f- area
d. area ~ force.
Answer:
c. force 4- area

Question 2.
The pressure exerted by a body of weight 200 N acting on an area of 5 m2 is
a. 50 Pa.
b. 200 Pa
c. 40 Pa
d. 0.02 Pa
Answer:
c. 40 Pa

Question 3.
The SI unit of pressure is –
a. dyne
b. newton
c. kilogram force
d. pascal.
Answer:
d. pascal.

Question 4.
One pascal is the same as –
a. 1 N2/m2
b. 1 N/m2
c. 1 N/m
d. 1 N/m
Answer:
b. 1 N/m2

Question 5.
Army tanks are provided with caterpillar tracks under their wheels in ordert to
a. decrease pressure on the ground
b. increase pressure on the ground
c. make them look different
d. prevent them from damage.
Answer:
a. decrease pressure on the ground

Question 6.
If the magnitude of force acting on a surface is doubled and area over which it acts is halved, then pressure exerted by the surface will
a. become twice
b. become four times
c. remain the same
d. be zero
Answer:
b. become four times

B. Fill in the blanks.

Question 1.
Pressure is directly proportional to
Answer:
Pressure is directly proportional to the magnitude of force applied.

Question 2.
For a given object, the pressure will decrease if the area of contact is
Answer:
For a given object, the pressure will decrease if the area of contact is increased.

Question 3.
If the force is increased keeping the area same, pressure will ………….
Answer:
If the force is increased keeping the area same, pressure will increase.

Question 4.
The straps and handles of travel bags are made broad to …………… the pressure on our shoulders.
Answer:
The straps and handles of travel bags are made broad to reduce the pressure on our shoulders.

Question 5.
An object exerts a pressure of 2 Pa on the ground. If another object of the same weight is kept above it, then the net pressure will become ………….
Answer:
An object exerts a pressure of 2 Pa on the ground. If another object of the same weight is kept above it, then the net pressure will become 4 Pa.

C. Match the following.

1. Increasing pressure a. broad straps of shoulder bags
2. Decreasing pressure b. thrust
3. Force acting per c. sharp tips of pins unit area
4. SI unit of pressure d. pressure
5. Magnitude of force e. pascal

Answer:

1. Increasing pressure c. sharp tips of pins unit area
2. Decreasing pressure a. broad straps of shoulder bags
3. Force acting per d. pressure
4. SI unit of pressure e. pascal
5. Magnitude of force b. thrust

D. State if the following statements are true or false. Correct the statement if it is false.

Question 1.
Pressure is increasingly proportional to the force applied.
Answer:
False. Pressure is directly proportional to the force applied.

Question 2.
Wooden sleepers are placed under railway tracks in order to increase pressure on the ground.
Answer:
False. Wooden sleepers are placed under railway tracks in order to decrease pressure on the ground.

Question 3.
Pressure is independent of the roughness of the surface in contact.
Answer:
False. Pressure is dependent on of the roughness of the surface in contact.

Question 4.
The pressure exerted by an object increases by oiling it.
Answer:
False. The pressure exerted by an object decreases by oiling it. _

Question 5.
Skis have a large surface in order to reduce the pressure on snow.
Answer:
True

E. Answer the following in a word or two or in a sentence.

Question 1.
What is the SI unit of pressure ?
Answer:
Pascal (Pa)

Question 2.
How are force, area of application of force and pressure related to each other ?
Answer:
Living Science Physics Class 6 ICSE Solutions Chapter 5 Pressure - 1

Question 3.
How is pressure effected if the force applied is doubled for the same area ?
Answer:
If the force applied is doubled for the same area, the pressure will also double.

F. Answer the following in short.

Question 1.
Why do safety pins and drawing pins have narrow and sharp tips ?
Answer:
Safety pins and drawing pins have narrow and sharp tips because the smaller surface area of the tip causes a high pressure and makes it easier for these pins to pierce through a given material.

Question 2.
Explain in brief why birds that walk on the leaves floating on the surface of water have wide feet.
Answer:
Wide feet increase the surface area and thus keep the pressure reduced and prevent birds from sinking.

Question 3.
Why do school bags have broad straps ?
Answer:
School bags have broad straps to increase the area of contact between shoulders and bag, thereby decreasing the pressure on the shoulders.

Question 4.
List any two applications of pressure.
Answer:
Applications of pressure :

  • Increasing pressure – Example : Knives, blades, scissors, etc have sharp edges as sharp edges have a small surface area. This increases the pressure and we can cut a given substance easily.
  • Decreasing pressure – Example : Heavy vehicles that carry huge loads in them are provided with extra tyres to increase the surface area and thus keep the pressure on the ground reduced.

G. Answer the following in detail.

Question 1.
Define pressure. Write the factors on which the pressure exerted by a body depends.
Answer:
Pressure is defined as the amount of force acting per unit area. It is denoted by P. Mathematically, it is expressed as
Living Science Physics Class 6 ICSE Solutions Chapter 5 Pressure - 2
Its unit is N/m2 or pascal (Pa).
Factors on which pressure exerted by a body depends are :
(i) Magnitude of force (thrust) – Greater the force, more is the pressure.
(ii) Area of contact – Greater the area of contact, lesser is the pressure.

Question 2.
What will be the effect of pressure on a body if the force applied on it becomes twice assuming that there is no change in area ?
Answer:
Since force applied on a body is directly proportional to the pressure on a body, if the force applied on it becomes twice, the pressure on it also becomes twice.

Question 3.
Where is pressure greater : 5 m below the surface of the sea or 10 m below the surface of the sea ?
Answer:
Pressure is greater at 10 m below the surface of the sea as the deeper we go in the sea, more is the weight of water on top and hence more is the force it applies and hence more pressure.

Question 4.
Why do the pillars of a bridge have a broad base and a narrow top ?
Answer:
Pillars supporting a bridge have broader bases and narraow ‘ tops to reduce pressure exerted on the ground by the enormous weight of the bridge.

Question 5.
How do high-rise building manage their pressure on the ground ?
Answer:
High rise buildings have massive weight and thus apply large force on the ground. In order to reduce the pressure exerted by them on the ground, they have a broad base.

H. Give reasons for the following.

Question 1.
Air pressure in the tubes of vehicles is maintained at an optimum level.
Answer:
If air pressure in the tubes would be more, then the tyres will inflate and their area of contact with the ground will decrease and it will exert more pressure and might burst. If air pressure is less, the tyres would deflate, area of contact with ground will increase and less pressure (less force) would lead to slow speed, more friction and wear and tear of the tires.

Question 2.
A blunt tip nail is generally discarded.
Answer:
A blunt tip nail has bigger area of contact which reduces the pressure and the effect of force is reduced. So, it won’t be easy to pierce it through a given material and hence discarded.

Question 3.
What would be the disadvantage if the arpiy tanks did not have catepillar tracks ?
Answer:
If the army tanks did not have caterpillar tracks, they would sink in the marshy areas. Their surface area of contact would be too less and they will exert more force and pressure on the ground.

I. Solve the: following numerical problems.

Question 1.
A box having a weight of 240 N is placed on a floor. If the area of its base in 8 m2, calculate the pressure exerted by the box on the floor.
Answer:
Force applied by the box on floor = 240 N Area of contact = 8 m2 Pressure exerted by the box on floor = ?
Force
We know, Living Science Physics Class 6 ICSE Solutions Chapter 5 Pressure - 1
P = \(\frac{240}{8 \mathrm{~m}^{2}}\)
= 30 N/m2 or 30 Pa

Question 2.
The tip of a drawing pin has an area of 0.01 mm2. Find the pressure exerted by it if a force of 20 N is applied on it.
Answer:
Area of contact = 0.01 mm2
Force applied on pin = 20 N
Pressure exerted by pin = ?
We know,
Pressure = Living Science Physics Class 6 ICSE Solutions Chapter 5 Pressure - 3
P = \(\frac{20 \mathrm{~N}}{0.01 \mathrm{~mm}^{2}}\) = 2000 N/mm2
= 2 x 109 N/m2 (1000 mm = lm)

Question 3.
A motorcycle weighs 1200 N. If the pressure exerted by one of its tyres is 120 Pa, then find the area of the tyre in contact with the road.
Answer:
Force applied by motorcycle on road = 1200 N
⇒ Force applied by one tyre on road = \(\frac {1200 N}{ 2 }\)
= 600 N
Pressure exerted by one tyre = 120 Pa
Area of contact of the tyre = ?
We know that, Pressure = Living Science Physics Class 6 ICSE Solutions Chapter 5 Pressure - 4
⇒ Area = Living Science Physics Class 6 ICSE Solutions Chapter 5 Pressure - 6 = \(\frac{600 \mathrm{~N}}{120 \mathrm{~N} / \mathrm{m}^{2}}\)
= 5 m2

Question 4.
A woman stands on high heels concentrating her weight on the tip of the heels. Calculate the pressure exerted by her heels on the ground if the area of contact of each heel is 2 cm2 and the weight of the woman is 650 N.
Answer:
Area of contact = 2 cm2
Force applied by woman on ground = 650 N
Pressure exerted by the heels on ground = ?
We know that,
Pressure = Living Science Physics Class 6 ICSE Solutions Chapter 5 Pressure - 5
⇒ P = \(\frac{650 \mathrm{~N}}{2 \mathrm{~cm}^{2}}\)
= 325 N/cm2
= 3250000 N/m2 [100 cm = 1 m]

Question 5.
A swimming pool of width 8 m and length 36 m is filled with water to a certain height. If the pressure exerted by the water on the bottom of the pool is 30,420 Pa, then find the force acting on the bottom of the pool.
Answer:
Area of swimming pool = 8m x 36 m = 288 m2
Pressure exerted by water = 30,420 Pa Force acting on the bottom of pool = ?
We know that,
Pressure = Living Science Physics Class 6 ICSE Solutions Chapter 5 Pressure - 7
Force = Pressure x Area
= 288m2 x 30,420 N/m2 [Pa = N/m2]
= 8,760,960 N

Living Science Physics Class 6 ICSE Solutions

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