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05. Simple Machine

Answers to textbook exercises

Prepared by: learnloophq@gmail.com

Last edited 26 days ago by Learn LoopHQ.

Chapter: 05. Simple Machine

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CHECK YOUR PROGRESS

Choose the correct option.

Mechanical advantage is the ratio of the load to the

a. effort.

Which of the following levers is always a force multiplier?

b. Lever of second order

Seesaw, crowbar and beam balance are the examples of

a. lever of first order.

Choose the correct option.

The windings in a screw are called

b. threads.

A door knob is an example of a

a. wheel and axle.

Which machines will you use for doing the following work?

To remove the lid of a tin can

Lever

To lift bricks to the top of a 12-storey building

Pulley (or Compound machine like a Crane)

To cut vegetables

Wedge

To hold papad for roasting

Lever (Tongs)

To draw water from a well

Pulley

EWABOABBOU

A. Choose the correct option.

Which of the following is an example of inclined plane?

a. Ramp

Which of the following is not a simple machine?

d. A bicycle

A screw jack required to lift a car to change a punctured tyre is an example of a

c. screw.

A screwdriver is an example of a/an

d. wheel and axle.

Which of the following is an example of a second class lever?

b. Nutcracker

A pulley is used because it

b. helps to apply effort in a convenient direction

Which of the following will make it easier to lift a heavy load on a wheelbarrow?

d. Both a and c

B. Name the following:

a rigid bar which can rotate freely about a fixed point or a fixed line

Lever

the ratio of load to effort of a machine

Mechanical Advantage

the work done on a machine

Input

the fixed point about which a lever can turn

Fulcrum

any plane surface that is tilted or inclined to the horizontal

Inclined plane

C. Fill in the blanks.

In a lever of the third order, the effort is always greater than the load.

The wheel of a pulley is supported within a frame called block.

Corkscrew is used to pull out a cork from a bottle of ketchup.

Moving parts of a machine are oiled to reduce friction.

The force applied to move an object by the lever is called effort.

D. Identify the class of the following levers.

A wheelbarrow being pushed.

Second order lever

A nutcracker with a nut.

Second order lever

A pair of pliers.

First order lever

A person rowing a boat.

Second order lever

E. Short answer type questions.

What is a simple machine? Name its different types.

A simple machine is a machine that is made up of very few parts and which simply changes the direction or the magnitude of force or helps us to work faster. Its different types are Lever, Inclined plane, Screw, Wedge, Wheel and axle, and Pulley.

What do you mean by load, effort and fulcrum of a machine?

Load (L) is the weight to be lifted or moved, that is, the force to be overcome by the machine. Effort (E) is the external force applied to lift or move the load. Fulcrum (F) is a fixed point about which the machine turns while doing mechanical work.

State the law of levers.

The law of levers states that when a lever is balanced, the product of the load and the load arm is equal to the product of the effort and the effort arm (Load × Load arm = Effort × Effort arm).

What is a pulley? Name its different types.

A pulley is a simple machine that consists of a wheel with a grooved rim, over which a rope or chain can be passed. Its different types are single fixed pulley and single movable pulley.

Define an inclined plane. Give two uses of inclined planes.

An inclined plane is simply a plane surface that is tilted or inclined to the horizontal. Two uses are ramps in multilevel parking lots and gradual slopes along hilly roads.

Give two examples each of a wedge, and a wheel and axle arrangement.

Two examples of a wedge are an axe and a knife. Two examples of a wheel and axle arrangement are a door knob and a steering wheel.

What is a screw? Give two uses of screws.

A screw is a modified inclined plane, resembling a nail with a spiral groove around it called threads. Two uses are to fasten two pieces of wood or metal and to pull out corks from bottles (corkscrew).

F. Long answer type questions.

What is an ideal machine and what is its efficiency? Why is this not achievable in practice?

An ideal machine is a frictionless machine where the work done on the machine (input energy) is equal to the work done by the machine (output energy). Its efficiency is 100%. This is not achievable in practice because some energy is always wasted due to friction between the moving parts of the machine, causing the output energy to always be less than the input energy.

Define the three kinds of levers. Draw diagrams to show the position of the fulcrum, load and effort in each of them.

Lever of the first order: The fulcrum (F) is between the load (L) and the effort (E). (e.g., Seesaw: L–F–E)

Lever of the second order: The load (L) is between the fulcrum (F) and the effort (E). (e.g., Wheelbarrow: F–L–E)

Lever of the third order: The effort (E) is between the fulcrum (F) and the load (L). (e.g., Human arm lifting a weight: F–E–L)

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

A single fixed pulley has its block attached to a support and does not move; its primary function is to change the direction of the effort. A single movable pulley has its block moving along with the load; it acts as a force multiplier, allowing a load to be lifted with half the effort, but requires the effort to be applied upwards.

List four steps to be taken for proper care of machines.

Four steps to be taken for proper care of machines are:

Machines should be cleaned regularly.

Moving parts of machines should be lubricated using oil to reduce friction, noise, and wear and tear.

The iron parts of the machines should be painted to prevent rusting.

When a machine is not in use, it should be kept covered to protect it from dust.

Higher Order Thinking Skills (HOTS)

Identify the five simple machines mentioned in the passage.

Baseball bat (Lever)

Plastic knives (Wedge)

Seesaws (Lever)

Slides (Inclined plane)

Arrows (the pointed tip acts as a Wedge)

Based on the levers identified above, write their order.

Baseball bat: Lever of the third order

Seesaws: Lever of the first order

Numericals

You use a lever with a mechanical advantage of 30. How heavy a load can you lift with an effort of 100 N?

Load = Mechanical Advantage × Effort = 30 × 100 N = 3000 N

The effort arm of a lever is 120 cm long and the load arm is 80 cm long. What is the effort needed to raise a load of 60 N weight? What is the mechanical advantage of this lever?

Effort needed: Load × Load arm = Effort × Effort arm 60 N × 80 cm = Effort × 120 cm Effort = 4800/120 = 40 N

Mechanical Advantage (MA): MA = Effort arm/Load arm = 120 cm/80 cm = 1.5

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