Force and Pressure class 8 question and answers workbook

1. Choose the correct option.

1. Which of the following expression is used to represent pressure?
2. Pressure=force x time ii. Pressure =force x area iii. Pressure = force÷ area iv. Pressure = force÷   time

Answer. (iii) Pressure = force ÷ area 

• Pressure at any point in a liquid depends on:
• Depth of the liquid at that  point.
• Mass of the liquid.
• Area of the container in which the liquid is kept.
• Height of the container in which the liquid is kept.

Answer. (i)Depth of the liquid at that point

• The SI unit of weight is :
• Joule
• Kilogram
• Newton
• Metre

Answer. (iii)Newton

• Which force explains only attraction between the objects?
• Gravitational force
• Frictional force
• Magnetic force
• Electrostatic force

Answer. (i)Gravitational force

Q2. Fill in the blanks.

1. A force exerted by a charged body on another charged or uncharged body is called  ________ force.

Answer. Electrostatic force

• Foundations of building are made broader to reduce the _____ on the ground.

Answer. Pressure 

• Pascal is the SI unit of ____

Answer. Pressure (1 Pascal = 1 N/m²)

• Air exerts _____ on the earth due to its weight.

Answer. Pressure (Atmospheric pressure due to air’s weight)

Q3. Define the following.

1. Contact force

Answer. Contact Force: A force applied through physical contact, e.g., pushing a box.

• Pressure

Answer. Pressure: Force per unit area (Formula: Pressure = Force/Area).

• Atmospheric pressure

Answer. Atmospheric Pressure: Pressure exerted by air molecules (≈101,325 Pa at sea level).

• Net force

Answer. Net Force: Combined effect of all forces acting on an object that changes its state of motion.

Q4. Answer the following questions in 2-3 sentences.

a.State any one application of the pressure exerted by liquids.

Answer. Hydraulic lifts use liquid pressure to lift heavy vehicles. Liquids transmit force equally in all directions (Pascal’s Law).

b.Dams are constructed with a vast base. Give a reason.

Answer. To reduce pressure on the ground. Larger area distributes the water’s force, preventing collapse.

c.What is a non-contact force? Name any two non-contact forces.

Answer. Forces acting without physical contact. Examples:

• Gravitational force (Earth pulling objects).
• Magnetic force (Magnets attracting iron).

d.Explain the working of a dropper with respect to the atmospheric pressure.

Answer. Squeezing the dropper expels air, reducing pressure inside. Higher atmospheric pressure outside pushes liquid into the dropper when released.

Q5. Solve the following numerical problems.Squeezing the dropper expels air, reducing pressure inside. Higher atmospheric pressure outside pushes liquid into the dropper when released.

a.A force of 60 N acts on an area of  120 m². What would be the pressure on the surface?

Answer. Given : Force= 60N,Area = 120msquare

Pressure = force/area =60N/120msquare

= 0.5 Pa

b. A solid object that weighs 270N is placed on a wooden plank of area 54 cm square. What would be the pressure on the wooden plank?

Answer. Given: Force =270 N ,Area =54 cm²

 convert to m^2: 54cm²

^{= 0.0054m square}

^{Pressure = 270N/ 0.0054 m square}

^{= 50,000 Pa}

c. What will be the area of the object on which the force of 500 N acts to produce a pressure of 35 Pa?

Answer. Answer. Given : Force= 500N, Pressure = 35Pa

Area = force/Pressure =500N/35 Pa

= 14.29 m²