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Selina solutions Selina ICSE Concise Physics for Class 10 chapter 3 Machines

Chapters

Selina Selina ICSE Concise Physics Class 10

Selina ICSE Concise Physics for Class 10

Chapter 3 - Machines

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State four ways in which machines are useful to us?

Name a machine for the following use to multiply force ?

Name a machine for the following use to change the point of application of force ?

Name a machine for the following use to change the direction of force ?

Name a machine for the following use to obtain gain in speed ?

What is the purpose of a jack in lifting a car by it?

What do you understand by an ideal machine? 

How Does Ideal Machine Differ from a Practical Machine ?

Explain the term mechanical advantage. State its unit.

Define the term velocity ratio, state its unit.

How is mechanical advantage related to the velocity ratio for an ideal machine?

Why is a machine not 100% efficient?

Define the term efficiency of a machine.

When does a machine act as a force multiplier ?

 When does a machine act as a speed multiplier ?

Can a machine act as a force multiplier and a speed multiplier simultaneously?

State the relationship between mechanical advantage, velocity ratio and efficiency. Name the
term that will not change for a machine of a given design.

Derive the relationship between mechanical advantage, velocity ratio and efficiency of a
machine.

State whether the efficiency of such a machine is equal to 1, less than 1 or more than 1.

How is the mechanical advantage related with the velocity ratio for an actual machine?

State reason why is mechanical advantage less than the velocity ratio for an actual machine.

State its principle ?

What is a lever ?

Write down a relation expressing the mechanical advantage of a lever.

Name the three classes of levers and distinguish between them. Give two examples of each class.

Give one example of a class I lever where mechanical advantage is more than one ?

Give one example of a class I lever where mechanical advantage is  less than one ?

What is the use of the lever if its mechanical advantage is less than I ?

Which one has the mechanical advantage less than 1 ?

A pair of scissors and a pair of pliers both belongs to the same class of levers. Name the class of lever ?

Explain why scissors for cutting cloth may have blades longer than the handles, but shears for cutting metals have short blades and long handles.

shows a uniform metre scale of weight W supported on a fulcrum at the 60 cm mark by applying the effort E at the 90 cm mark.

state with reason whether the weight W of the scale is greater than, less than or equal to the effort E.

Find the mechanical advantage in an ideal case.

Reason: The weight W of a uniform metre scale acts at 50 cm mark. Since distance of weight of scale from fulcrum F is less then that of the effort E., so the weight W of scale is greater than the effort E.

Which type of lever has a mechanical advantage always more than one? Give one example .

What change can be made in this lever to increase its mechanical advantage?

Draw a diagram of a lever which is always used as a force multiplier. How is the effort arm related to the load arm in such a lever?

Explain why the mechanical advantage of a Class II type of lever is always more than 1.

Draw a labelled diagram of a class II lever. Give one example of such a lever.

show a nut cracker In the diagram, mark the position of the fulcrum F and the line of action of load L and effort E .

shows a nut cracker name the class of lever ?

The diagram below shows a wheel barrow. Mark position of fulcrum F and draw arrows to show the directions of load L and effort E. What class of lever is the whell barrow? Give one more example of the same class of lever.

State the kind of lever which always has the mechanical advantage less than 1. Draw a labelled diagram of such lever.

Explain why the mechanical advantage of the class III type of lever is always less than 1.

Class III levers have mechanical advantage less than one. Why are they then used?

What type of lever is formed by the human body while raising a load on the palm ?

What type of lever is formed by the human body while raising the weight of body on toes?

Indicate the positions of load, effort and fulcrum in the forearm shown below in Fig 3.15 Name class of lever.

Draw a labelled sketch of a class III lever.

 

Give one example of class III lever kind of lever.

Give example of each class of lever in a human body?

State the class of levers and the relative positions of load (L) effort (E) and fulcrum (F) in  a bottle opener ?

State the class of levers and the relative positions of load (L) effort (E) and fulcrum (F) in sugar tongs .

Draw Diagrams to illustrate the position of fulcrum load and effort, in the following :

A seesaw .

Draw Diagrams to illustrate the position of fulcrum load and effort, in the following:

A common balance .

Draw Diagrams to illustrate the position of fulcrum load and effort, in the following:

A nut cracker .

Draw Diagrams to illustrate the position of fulcrum load and effort, in the following:

Forceps .

Classify the following into lever as class I, class II or class III of  a door ?

Classify the following into lever as class I, class II or class III  of a catapult ?

Classify the following into lever as class I, class II or class III of a wheel barrow ?

Classify the following into lever as class I, class II or class III of a fishing rod ?

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Mechanical advantage (M.A), load (L) and effort (E) are related as :
(a) M.A. = × E
(b) M.A × E = L
(c) E = M.A. × L
(d) None of these

The correct relationship between the mechanical advantage (M.A), the velocity ratio (V.R) and the efficiency (n) is:
(a) M.A. = η × v.r.
(b) V.R. = η × M.A.
(c) η = M.A. × V.R.
(d) None of these

Which of the following statements is not true for a machine:
(a) It always has efficiency less than 100%
(b) its mechanical advantage can be less than 1.
(c) It can also be used as a speed multiplier
(d) It can have a mechanical advantage greater than the velocity ratio.

The lever for which the mechanical advantage is less than 1 has:
(a) fulcrum at mid-point between load and effort.
(b) Load between effort and fulcrum
(c) effort between fulcrum and load
(d) Load and effort acting at the same point

Class II levers are designed to have:
(a) M.A. = V.R.
(b) M.A. > V.R.
(c) M.A > 1
(d) M.A < 1

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A crowbar of length 120 cm has its fulcrum situated at a distance of 20 cm from the load. Calculate the mechanical advantage of the crowbar.

A 4 m long rod of negligible weight is to be balanced about a point 125 cm from one end. A load of 18 kgf is suspended at a point 60 cm from the support on the shorter arm :
A weight W is placed 250 cm from the support on the longer arm Find W ?

A 4 m long rod of negligible weight is to be balanced about a point 125 cm from one end. A load of 18 kgf is suspended at a point 60 cm from the support on the shorter arm :

If W = 5 kgf, where must it be kept to balance the rod ?

A 4 m long rod of negligible weight is to be balanced about a point 125 cm from one end. A load of 18 kgf is suspended at a point 60 cm from the support on the shorter arm :

To which class of lever does it belong ?

A pair of scissors has its blades 15 cm long, while its handles are 7.5 cm long. What is its mechanical advantage?

A force of 5 kgf is required to cut a metal sheet. A shears used for cutting the metal sheet has its blades 5 cm long, while its handles is 10 cm long. What effort is needed to cut the sheet?

Fig 3.16 below shows a lever in use.

(a) To which class of lever does it belong?
(b) If AB = 1m, AF = 0.4 m, find its mechanical advantage,
(c) calculate the value of E.

A man uses a crowbar of length 1.5 m to raise a load of 75 kgf by putting a sharp edge below the bar at a distance 1 m from his hand. Draw a diagram of the arrangement showing the fulcrum (F), load (L) and effort (E) with their directions. State the kind of lever. Calculate: (1) load arm, (2) effort arm, (3) mechanical advantage and (4) the effort needed.

A pair of scissors is used to cut a piece of a cloth by keeping it at a distance 8.0 cm from its rivet and applying an effort of 10 kgf by fingers at a distance 2.0 cm from the rivet. (a) Find : (i) the mechanical advantage of scissors and (ii) the load offered by the cloth (b) How does the pair of scissors act: as a force multiplier or as speed multiplier?

Fig 3.17 below shows a lever in use.

(a) To which class of lever does it belong?
(b) If FA = 80 cm, AB = 20 cm, find its mechanical advantage.
(c) Calculate the value of E.

Fig 3.18 below shows the use of a lever.

State the principle of moments as applied to the above lever.

Fig 3.18 below shows the use of a lever.

Give an example of this class of lever.

Fig 3.18 below shows the use of a lever.

If FA = 10 cm, AB = 500 cm calculate: (i) the mechanical advantage and (ii) the minimum effort required to lift the load.

Fig 3.19 below shows a wheel barrow of mass 15 kg carrying a load of 30 kgf with its centre of gravity at A. The points B and C are the centre of wheel and tip of the handle such that the horizontal distance AB = 20 cm and AC = 40 cm.

Calculate: (i) the load arm, (ii) the effort arm, (iii) the mechanical advantage and (iv) the minimum effort required to keep the leg just off the ground.

A fire tongs has arms 20 cm long. Its is used to lift a coal of weight 1.5 kgf by applying an effort at a distance 15 cm from the fulcrum. Find: (i) the mechanical advantage of fire tongs and (ii) the effort needed.

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Give two examples  of inclined plane where it us used to raise a heavy load with less effort ?

What is an inclined plane?

‘The force needed to push a load up an inclined plane is less than the force needed to lift it directly’ Give a reason.

Write an expression for the mechanical advantage of an inclined plane in terms of its length I and vertical height h.

State whether the mechanical advantage of an inclined plane is equal to 1, less than 2 or greater than 1?

Explain  gear system its working .

What is a gear system ?

Explain how a gear system can be used to obtain gain in speed ?

Explain how a gear system can be used to obtain gain in torque ?

Explain how a gear system can be used to obtain Change in direction of rotation.  Given one example for each .

Define the following term in reference to a gear system of Driving gear ?

Define the following term in reference to a gear system for Driven gear ?

Define the following term in reference to a gear system for Gear ratio ?

Define the following term in reference to a gear system for Gain in speed ?

Define the following term in reference to a gear system for Gain in torque ?

What should be the gear ration of a car : equal to 1, less than 1 or greater than 1, while gaining speed on the road ?

What should be the gear ration of a car : equal to 1, less than 1 or greater than 1, while ascending a hill ?

In a gear system, the gear ration of the driving wheel A and driven wheel B is 10:1. To rotate the driven wheel B in the direction of driving wheel A, the driving wheel A is engaged with other wheel C. what should be the gear ratio of the wheels A and C?

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The mechanical advantage of an inclined place is always:
(a) less than 1
(b) equal to 1
(c) greater than 1
(d) nothing can be said

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A boy has to lift a load of mass 50 kg to a height of 1 m. (a) what effort is required if he lifts it directly? Take g = 10 N kg-1 (b) If the boy can exert a maximum effort of 250 N, so he uses an inclined plane to lift the load up. What should be the minimum length of the plank used by him?

A coolie uses a sloping wooden plank of length 2.0 m to push up a drum of mass 100 kg into the truck at a height 1.0 m.
(a) What is the mechanical advantage of the sloping plank?
(b) How much effort is needed to push the drum up into the truck?
What assumption have you made in arriving at the answer in part (b) above?

A gear system has one wheel with 10 teeth and the other wheel with 50 teeth. Calculate the gain in speed and the gain in torque that you can obtain using them. What will be the gear ration in each case?

A gear system has the driving wheel of radius 2 cm and driven wheel of radius 20 cm.
(a) Find the gear ratio.
(b) If the number of rotations made per minute by the driving wheel is 100, find the number of rotations per minute made by the driven wheel.
(c) If the driven wheel has 40 teeth, find the number of teeth in the driving wheel.

The driving wheel of a gear system is of radius 1 cm and it has 8 teeth. For twelve rotations of
the driving wheel, if the driven wheel makes one rotation find :
(a) The radius, and
(b) the number of teeth in the driven wheel.

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What is a single fixed pulley? State its one use.

What is the ideal mechanical advantage of a single fixed pulley? Can it be used as a force
multiplier?

Name the pulley which has no gain in mechanical advantage. Explain, why is such a pulley then used?

What is the velocity ratio of a single fixed pulley?

In a single fixed pulley, if the effort moves by a distance x downwards, by what height is the load raised upwards?

What is a single movable pulley? What is its mechanical advantage in the ideal case?

Name the type of single pulley that can act as a force multiplier. Draw a labelled diagram of the pulley mentioned by you.

Give two reasons why the efficiency of a single movable pulley system is not 100%

In which direction the force need to applied, when a single pulley is used with a mechanical advantage greater than one? How can you change the direction of force applied without altering its mechanical advantage? Draw a labelled diagram of the system.

What is the velocity ratio of a single movable pulley?

In a single movable pulley, if the effort moves by a distance x upwards, by what height is the load raised?

Draw a labelled diagram of an arrangement of two pulleys, one fixed and other movable. In the diagram, mark the directions of al forces acting on it. What is the ideal mechanical advantage of the system? How can it be achieved?

The diagram below shows a pulley arrangement.
(a) In the diagram, mark the direction of tension on each strand of string.
(b) What is the purpose of the pulley B?

(c) If the tension is T, Deduce the relation between T and E.
(d) What is the velocity ratio of the arrangement?
(e) Assuming that the efficiency of the system is 100%, What is the mechanical advantage?


 

Differentiate between a single fixed pulley and a single movable pulley.

The Diagram alongside shows an arrangement of three pulleys A, B, and C. The load is marked as L and the effort as E.
(a) Name the Pulleys A, B, and C.
(b) Mark in the diagram the directions of load (L), effort (E) and tension T1 and T2 in the two strings.
(c) How are the magnitudes of L and E related to the tension T1?
(d) Calculate the mechanical advantage and velocity ratio of the arrangement.
(e) What assumptions have you made in parts (c) and (d)?

Draw a diagram of combination of three movable pulleys with a fixed pulley showing the directions of load, effort and tension in each strand. Find: (i) mechanical advantage, (ii) Velocity ration and (iii) efficiency of the combination in ideal situation.

Extra questions

What do you understand by a simple machine?

Selina Selina ICSE Concise Physics Class 10

Selina ICSE Concise Physics for Class 10
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