[2 Mark Question Answer]

Question 12 Marks

A , B and C are three forces each of magnitude 5 N acting in the plane of paper as shown in the figure. Point O lies in the same plane.
Complete the table using the labels from the figure. The first label is done for you.

S.No.	Description	Label
(a)	The force having the greatest moment about O	A
(b)	The force having the least moment about O
(c)	The forces producing clockwise moment
(d)	The forces producing anticlockwise moment
(e)	The forces producing anticlockwise moment O

Answer

S.No.	Description	Label
(a)	The force having the greatest moment about O	A
(b)	The force having the least moment about O	C
(c)	The forces producing clockwise moment	A and B
(d)	The forces producing anticlockwise moment	V
(e)	The forces producing anticlockwise moment O	5.5 Nm (clockwise)

[Hint: Clockwise moment = 5 x 0.9 + 5 x 0.7 4.5+3.5 8.0 Nm
Anticlockwise moment 5 x 0.5=2.5 Nm
$\therefore$Resultant torque 8.0 Nm2.5 Nm 5.5 Nm (clockwise)]

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Question 22 Marks

A uniform metre scale balances horizontally on a knife edge placed at 55 cm mark, when a mass of 25 g is supported from one end. Draw the diagram of the arrangement. Calculate mass of the scale.

Answer

As the metre scale is uniform, its weight acts at 50 cm mark. Taking moments about 55 cm mark.
Moments in CWD $=45 cm \times 25 g$
Moments in $ACWD = W \times 5 cm$
By the law of moments,
$\begin{aligned} 45 cm \times 25 g & = W \times 5 cm \\ \therefore W & =\frac{45 cm \times 25 g}{5 cm}=225 g\end{aligned}$

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Question 32 Marks

The diagram alongside shows a force $F =5 N$ acting at point A produces a moment of force of 6 Nm about point O . What is the diameter of the wheel?

Answer

$F =5 N$; Moment of foree $=6 Nm$
$\perp$ distance $=\frac{\text { Moment of force }}{\text { Force }}=\frac{6 Nm }{5 N}=1.2 m$
Now, OA = Radius of the wheel $=1.2 m$
$\therefore$ Diameter of the wheel $=2 \times$ radius $=2 \times 1.2 m=2.4 m$

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Question 42 Marks

Define
(a) Circular motion (b) Centripetal force (c) Centrifugal force

Answer

(a) Circular motion - The motion of a body in a circular path with uniform speed but variable velocity, such that it is acted upon by an acceleration is called circular motion.
(b) Centripetal force - A force which is directed towards the centre of a circular path and always acts at right angles to the direction of motion is called centripetal force,
(c) Centrifugal force - The force acting on a body away from the centre of its circular path along the radius is called centrifugal force,

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Question 52 Marks

Explain the following
(a) Why does a jack screw provided with a long arm?
(b) It is easier to turn a steering wheel of larger diameter than a steering wheel of small diameter.

Answer

(a) The long arm of the jackscrew acts as the perpendicular distance between the line of action of force and the axis of rotation. This generates maximum moment of force for a minimum effort applied.
(b) Steering wheel of a larger diameter ensures maximum perpendicular distance between the line of action of force and the axis of rotation. This helps in turning the steering wheel with minimum effort.

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Question 62 Marks

What do you understand by the following terms
(a) Couple (b) Arm of couple (c) Moment of couple

Answer

(a) Couple - Two equal and opposite forces acting on a rigid body, such that they act along different lines of action of force constitute a couple.
(b) Arm of couple - The perpendicular distance between the two equal and opposite forces is called the arm of couple.
(c) Moment of couple - Moment of couple is the product of any one of the force and the arm of couple.

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Question 72 Marks

(a) What do you understand by the term moment of force?
(b) State two factors which determines the moment of force.

Answer

(a) The product of the magnitude of force and the perpendicular distance between the point of application of force and the turning point or axis of rotation is called moment of force.
(b) The moment of force is directly proportional to:
(i) magnitude of force applied.
(ii) the perpendicular distance between the point of application of force and the turning point.

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Question 82 Marks

Define the following:
(a) Rigid body
(b) Principal of transmissibility of force

Answer

(a) Rigid body: Rigid body is a body which does not deform under application of an external force.
(b) Principle of transmissibility of force - The point of action of force can be transmitted anywhere along the line of action of force, without causing any material difference in the movement of the body.

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Physics [2 Mark Question Answer]

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