Class 10 Force Mock Test (ICSE)

Topics in Force

• Moment of a force and couple
• Principle of moments
• Centre of gravity
• Uniform circular motion
• Centripetal and centrifugal force

Force practice questions with answers

1. Q1Multiple choice·1 mark
   According to the principle of moments, when a body is in rotational equilibrium:

   1. (a)Total force acting on the body is zero
   2. (b)Total upward force = Total downward force
   3. (c)Clockwise moment is greater than anticlockwise moment
   4. (d)Total clockwise moment = Total anticlockwise moment
   Show answer and step marks

   1. Correct option: (d) Total clockwise moment = Total anticlockwise moment. This defines the condition of rotational equilibrium.+1

   Answer: (d)
2. Q2Multiple choice·1 mark
   Centrifugal force is considered a fictitious or pseudo force experienced by an observer in:

   1. (a)a state of uniform linear motion
   2. (b)free fall under gravity
   3. (c)a non-inertial frame of reference
   4. (d)an inertial frame of reference
   Show answer and step marks

   1. Correct option: (c) a non-inertial frame of reference. Centrifugal force appears only when observations are made from an accelerating or rotating (non-inertial) frame.+1

   Answer: (c)
3. Q3Multiple choice·1 mark
   Which of the following physical quantities remains constant during the uniform circular motion of a body?

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

   1. Correct option: (b) Speed. In uniform circular motion, the magnitude of velocity (speed) remains constant while direction changes continuously.+1

   Answer: (b)
4. Q4Multiple choice·1 mark
   The SI unit of the moment of a force is:

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

   1. Correct option: (d) $\text{N m}$. The SI unit of the moment of a force is Newton-metre.+1

   Answer: (d)
5. Q5Long answer·4 marks
   (a) What is meant by uniform circular motion? Is it an accelerated motion? Give a reason to support your answer. (b) A stone of mass $200\text{ g}$ is tied to the end of a string and whirled in a horizontal circle of radius $1.5\text{ m}$ with a constant speed of $3\text{ m s}^{-1}$. Calculate the magnitude of the centripetal force acting on the stone.
   Show answer and step marks

   1. (a) Definition: When a body moves with a constant speed in a circular path, its motion is called uniform circular motion.+1
   2. (a) Acceleration reason: Yes, it is an accelerated motion because the direction of motion changes continuously at every point, resulting in a variable velocity.+1
   3. (b) Formula and substitution: $F_c = \frac{mv^2}{r} = \frac{0.2 \times 3^2}{1.5}$+1
   4. (b) Final calculation: $F_c = \frac{0.2 \times 9}{1.5} = 1.2\text{ N}$+1

   Answer: (a) Motion of a body along a circular path with constant speed; yes, it is accelerated because the direction of motion, and hence the velocity, changes continuously. (b) $F_c = 1.2\text{ N}$
6. Q6Long answer·4 marks
   (a) State whether any work is done by the centripetal force acting on a body moving in a circular path with a constant speed. Give a reason for your answer. [1] (b) A stone of mass $0.5\text{ kg}$ is tied to one end of a string of length $1.5\text{ m}$ whose other end is fixed to a peg on a smooth horizontal table, and the stone is whirled round the peg in a horizontal circle on the table with a constant speed of $6\text{ m s}^{-1}$. Calculate the tension in the string. [2] (c) State one difference between uniform linear motion and uniform circular motion with respect to acceleration. [1]
   Show answer and step marks

   1. (a) No work is done because the centripetal force is always perpendicular to the instantaneous displacement of the body.+1
   2. (b) Stating or using the formula for tension (centripetal force): $T = \frac{m v^2}{r}$ with correct substitution of values.+1
   3. (b) Simplifying and calculating the final value: $T = \frac{0.5 \times 6^2}{1.5} = 12\text{ N}$.+1
   4. (c) In uniform linear motion, acceleration is zero, whereas in uniform circular motion, acceleration is non-zero due to the continuous change in the direction of velocity.+1

   Answer: (a) No work is done; (b) $12\text{ N}$; (c) Acceleration is zero for uniform linear motion and non-zero for uniform circular motion.

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