Class 9 Laws of Motion Mock Test (ICSE)

Topics in Laws of Motion

• Contact and non-contact forces
• Newton's first law and inertia
• Linear momentum and Newton's second law
• Newton's third law
• Gravitation and acceleration due to gravity
• Mass and weight

Laws of Motion practice questions with answers

1. Q1Multiple choice·1 mark
   Inertia of an object is a direct measure of its:

   1. (a)Acceleration
   2. (b)Velocity
   3. (c)Mass
   4. (d)Weight
   Show answer and step marks

   1. Correct option: (c) Mass+1

   Answer: (c)
2. Q2Multiple choice·1 mark
   Action and reaction forces according to Newton's third law:

   1. (a)Act on different bodies in opposite directions
   2. (b)Have unequal magnitudes but the same direction
   3. (c)Do not depend on each other under any circumstance
   4. (d)Act on the same body and cancel each other out
   Show answer and step marks

   1. Correct option: (a) Act on different bodies in opposite directions+1

   Answer: (a)
3. Q3Multiple choice·1 mark
   Which of the following is an example of a non-contact force?

   1. (a)Normal reaction force
   2. (b)Gravitational force
   3. (c)Tension in a string
   4. (d)Frictional force
   Show answer and step marks

   1. Correct option: (b) Gravitational force+1

   Answer: (b)
4. Q4Multiple choice·1 mark
   The SI unit of linear momentum is:

   1. (a)$\text{kg m}^2\text{s}^{-1}$
   2. (b)$\text{kg m s}^{-2}$
   3. (c)$\text{kg m s}^{-1}$
   4. (d)$\text{N m}$
   Show answer and step marks

   1. Correct option: (c) $\text{kg m s}^{-1}$+1

   Answer: (c)
5. Q5Long answer·4 marks
   (a) State two differences between mass and weight of a body. (b) An object has a mass of $50\text{ kg}$ on the surface of the Earth. Taking the acceleration due to gravity on Earth as $9.8\text{ m s}^{-2}$ and on the Moon as one-sixth of that on Earth, calculate: (i) the mass of the object on the Moon, (ii) the weight of the object on the Earth and on the Moon.
   Show answer and step marks

   1. (a) First difference, any one of: mass is the quantity of matter in a body, while weight is the force with which the Earth attracts it; mass stays the same everywhere, while weight changes with the acceleration due to gravity; mass is a scalar, while weight is a vector; the SI unit of mass is kilogram ($\text{kg}$), while that of weight is newton ($\text{N}$); mass is measured with a beam (physical) balance, while weight is measured with a spring balance; or any other valid difference.+1
   2. (a) Second difference, a different one from the same list.+1
   3. (b)(i) Mass on the Moon = $50\text{ kg}$ (mass does not change with location).+1
   4. (b)(ii) Weight on Earth = $50\text{ kg} \times 9.8\text{ m s}^{-2} = 490\text{ N}$.+0.5
   5. (b)(ii) Weight on Moon = $50 \times \frac{9.8}{6} = 81.67\text{ N}$ (or $490\text{ N} \div 6$).+0.5

   Answer: (a) Any two of: mass is the quantity of matter while weight is the Earth's pull on it; mass is constant everywhere while weight varies with $g$; mass is a scalar while weight is a vector; mass is in $\text{kg}$ while weight is in $\text{N}$; mass is measured by a beam balance while weight is measured by a spring balance. (b)(i) $50\text{ kg}$, (b)(ii) $490\text{ N}$ on Earth and $81.67\text{ N}$ on the Moon.

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