Q1 State the condition when on applying a force, a body has:
(a) translational motion
(b) rotational motion.

solutions

Q2 Define moment of force and state its S.I. unit.

solutions

Q3 State whether the moment of force is a scalar or vector quantity?

solutions

Q4 State two factors affecting the turning effect of a force.

solutions

Q5 When does a body rotate? State one way to change the direction of rotation of a body. Give a suitable example to explain your answer.

solutions

Q6 Write the expression for the moment of force about a given axis

solutions

Q7 What do you understand by the clockwise and anticlockwise moment of force? When is it taken positive?

solutions

Q8 State one way to reduce the moment of a given force about a given axis of rotation

solutions

Q9 State one way to obtain a greater moment of a force about a given axis of rotation.

solutions

Q10 Why is it easier to open a door by applying the force at the free end of it?

solutions

Q11 The stone of hand flour grinder is provided with a handle near its rim. Give a reason

solutions

Q12 It is easier to turn the steering wheel of a large diameter than that of a small diameter. Give reason.

solutions

Q13 A spanner (or wrench) has a long handle. Why?

solutions

Q14 A jack screw is provided with a long arm. Explain why?

solutions

Q15 A, B and C are the three forces each of magnitude 4N acting in the plane of paper as shown in figure. The point O lies in the same plane.

(i) Which force has the least moment about O? Give reason.
(ii) Which force has the greatest moment about O? Give reason.
(iii) Name the forces producing (a) clockwise, (b) anticlockwise moments.
(iv) What is the resultant torque about the point O?

solutions

Q16 The adjacent diagram shows a heavy roller, with its axle at O, which is to be raised on a pavement XY. If there is friction between the roller and pavement, show by an arrow on the diagram the point of application and the direction of force to be applied. If pivoted at 0, now will it go up?

solutions

Q17 A body is acted upon by two forces each of magnitude F, but in opposite directions. State the effect of the forces if
(a) both forces act at the same point of the body.
(b) the two forces act at two different points of the body at a separation r.

solutions

Q18 Draw a neat labelled diagram to show the direction of two forces acting on a body to produce rotation in it. Also mark the point O about which the rotation takes place.

solutions

Q19 What do you understand by the term couple? State its effect on a body. Give two examples in our daily life where couple is applied to turn a body.

solutions

Q20 Define the moment of a couple. Write its S.I unit.

solutions

Q21 Prove that
Moment of couple = Force x Couple arm.

solutions

Q22 What do you mean by equilibrium of a body?

solutions

Q23 State the condition when a body is in
(i) static equilibrium.
(ii) dynamic equilibrium.
Give one example each of static and dynamic equilibrium.

solutions

Q24 State two conditions for a body, acted upon by several forces to be in equilibrium.

solutions

Q25 State the principle of moments. Name one device based on it.

solutions

Q26 Describe a simple experiment to verify the principle of moments, if you are supplied with a metre rule, a fulcrum and two springs with slotted weights.

solutions

Q27 Complete the following sentences:
(i) The S.I. unit of moment of force is ________
(ii) In equilibrium algebraic sum of moments of all forces about the point of rotation is _________.
(iii) In beam balance when the beam is balanced in a horizontal position, it is in ________ equilibrium.
(iv) The moon revolving around the earth is in _________ equilibrium.

solutions

Multiple Choice type Questions :

Q1 The moment of a force about a given axis depends:
1. only on the magnitude of force
2. only on the perpendicular distance of force from the axis
3. neither on the force nor on the perpendicular distance of force from the axis
4. both, on the force and its perpendicular distance from the axis.

solutions

Q2 A body is acted upon by two unequal forces in opposite directions, but not in the same line. The effect is that:
1. the body will have only the rotational motion
2. the body will have only the translational motion
3. the body will have neither the rotational motion nor the translational motion
4. the body will have rotational as well as translational motion.

solutions

Numericals

Q1 The moment of a force of 10N about a fixed point O is 5Nm. Calculate the distance of the point O from the line of action of the force

solutions

Q2 A nut is opened by a wrench of length 10cm. If the least force required is 5.0N, find the moment of force needed to turn the nut.

solutions

Q3 A wheel of diameter 2m is shown in figure with axle at O. A force F = 2N is applied at B in the direction shown in figure

Calculate the moment of force about
(i) the centre O, and
(ii) the point A.

solutions

Q4 The diagram shows two forces F₁ = 5N and F₂ = 3N acting at points A and B of a rod pivoted at a point O, such that OA = 2m and OB = 4m

Calculate:
(i) the moment of force F₁ about O.
(ii) the moment of force F₂ about O.
(iii) total moment of the two forces about O.

solutions

Q5 Two forces each of magnitude 10N act vertically upwards and downwards respectively at the two ends A and B of a uniform rod of length 4m which is pivoted at its mid-point O as shown. Determine the magnitude of resultant moment of forces about the pivot O.

solutions

Q6 Figure shows two forces each of magnitude 10N acting at the points A and B at a separation of 50 cm, in opposite directions. Calculate the resultant moment of the two forces about the point (i) A, (ii) B and (iii) O, situated exactly at the middle of the two forces.

solutions

Q7 A steering wheel of diameter 0.5m is rotated anti-clockwise by applying two forces each of magnitude 5N. Draw a diagram to show the application of forces and calculate the moment of forces applied.

solutions

Q8 A uniform metre rule is pivoted at its mid-point. A weight of 50 gf is suspended at one end of it. Where should a weight of 100gf be suspended to keep the rule horizontal?

solutions

Q9 A uniform metre rule balances horizontally on a knife edge placed at the 58 cm mark when a weight of 20gf is suspended from one end. (i) Draw a diagram of the arrangement. (ii) What is the weight of the rule?

solutions

Q10 The diagram shows a uniform bar supported at the middle point O. A weight of 40 gf is placed at a distance 40cm to the left of the point O. How can you balance the bar with a weight of 80 gf?

solutions

Q11 Figure shows a uniform metre rule placed on a fulcrum at its mid-point O and having a weight 40gf at the 10 cm mark and a weight of 20 gf at the 90 cm mark.
(i) Is the metre rule in equilibrium? If not, how will the rule turn?
(ii) How can the rule be brought in equilibrium by using an additional weight of 40gf?

solutions

Q12 When a boy weighing 20 kgf sits at one end of a 4m long see-saw, it gets depressed at its end. How can it be brought to the horizontal position by a man weighing 40 kgf.

solutions

Q13 A physical balance has its arms of length 60 cm and 40 cm. What weight kept on a pan of longer arm will balance an object of weight 100 gf kept on other pan?

solutions

Q14 The diagram shows a uniform meter rule weighing 100 gf, pivoted at its centre O. Two weights 150gf and 250gf hang from the point A and B respectively of the metre rule such that OA = 40 cm and OB = 20 cm.
Calculate:
(i) the total anticlockwise moment about O,
(ii) the total clockwise moment about O,
(iii) the difference of anticlockwise and clockwise moment, and
(iv) the distance from O where a 100gf weight should be placed to balance the metre rule.

solutions

Q15 A uniform metre rule of weight 10 gf is pivoted at its 0 mark.
(i) What moment of force depresses the rule?
(ii) How can it be made horizontal by applying a least force?

solutions

Q16 A uniform half metre rule can be balanced at the 29.0 cm mark when a mass 20g is hung from its one end.
(a) Draw a diagram of the arrangement.
(b) Find the mass of the half metre rule.
(c) In which direction would the balancing point shift if 20g mass is shifted inside from its one end?

solutions

Q17 A uniform metre rule of mass 100 g is balanced on a fulcrum at mark 40 cm by suspending an unknown mass m at the mark 20 cm.
(i) Find the value of m.
(ii) To which side the rule will tilt if the mass m is moved to the mark 10 cm?
(iii) What is the resultant moment now?
(iv) How can it be balanced by another mass 50 g?

solutions

Q18 In figure below, a uniform bar of length l m is supported at its ends and loaded by a weight W kgf at its middle. In equilibrium, find the reactions R₁ and R₂ at the ends.

solutions