Physics
Some of the facts that you have learnt till now are listed below. Tick (✓) the facts that are correct and cross (x) the facts that are incorrect.
(a) Efficiency of a machine can be 100%.
(b) A wheel and axle move together.
(c) A wedge is a combination of an axle and inclined plane.
(d) Screw acts as a fastener.
(e) Screwdriver is an example of screw.
Machines
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Answer
(a) x
Corrected Fact — The efficiency of every machine used by us is always less than 100% as some of the input energy is used up in overcoming the friction between different parts of the machine and as heat from the working parts of the machine. Therefore, output energy is always less than the input energy and hence, in reality the efficiency can never be 100%.
(b) ✓
(c) x
Corrected Fact — A wedge is a combination of two inclined planes.
(d) ✓
(e) x
Corrected Fact — Screwdriver is an example of wheel and axle.
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Related Questions
Identify the types of lever in the given simple machines.
Solve the following numericals.
(a) What is the mechanical advantage of a machine that lifts a load of 100 N with an effort of 20 N?
(b) What is the effort required if the mechanical advantage is 9 and the load is 81 N?
Fill in the blanks.
(a) The ratio of the load lifted by a machine to the effort applied on it is called …………… .
(b) Work done on an object is the product of …………… and …………… .
(c) There are three types of levers based on the positions of ……………, …………… and …………… .
(d) The ratio of work done by a machine to the work done on the machine is termed as …………… of the machine.
(e) The arrangement of several pulleys to pick heavy loads is called …………… .
State whether the following statements are true or false. Correct the false statements.
(a) A girl riding a bicycle is getting zero work done.
(b) When the value of mechanical advantage is equal to one, it means that effort is equal to load.
(c) In class III lever, the fulcrum is between the load and the effort.
(d) In a fixed pulley, the pulley can move.
(e) Tyres of cars and buses are examples of wheel and axle.