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Reason: 2 Marks
Problems: 3 Marks
Since the tape is stretchable and when you will measure anything it will give inaccurate measurements. Therefore we cannot use it for measuring purposes.
Problems:
1. While measuring a distance, we need to tell someone how much tape has been stretched which is difficult to measure. It leads to incorrect measurements.
2. We cannot measure manually how much the tape has been stretched.
3. If you measure the length of an object twice using an elastic tape, then you may get different values of the same length each time. This is because elastic tapes are stretchable.

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Some of the reasons for the difference in their measurement could be:
1. Different measuring devices were used.
2. The smallest length that could be measured by different devices may be different.
3. The measurement may not be along the shortest length in all the three cases.
4. The end of the corridor may not be easily accessible.
5. The measuring devices may be faulty (not standardized).

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Rest: 1 Mark
Motion: 1 Mark
The bodies, which don’t change their positions over time, are said to be at rest. The objects, which change their positions over time, are said to be in motion.

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The motion of an object along a straight line is termed as rectilinear motion whereas motion along a circular path is termed as circular motion. Various parts of a bicycle moving along a straight road shows different forms of motion. However, the overall motion is considered as rectilinear motion.
(i) Handlebar and seat: Handlebar and seat moves in a straight line. So they possess rectilinear motion.
(ii) Pedal: Pedal moves in a circular path, so it possescircular motion.
(iii) Wheel: Since wheels of thebicycle moves in a straight line by rotating itself, it has both circular and rectilinear motion.

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Each Point: 1 Mark
1) Rectilinear motion
2) Circular motion
3) Rectilinear motion

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Significance of measurement: 2 Marks
Examples: 1 Mark
Measurement helps us to compare unknown quantities with the known quantities. Measurement helps us make quantitative statements about how big, how long, how fast things are. Without measurement, the final product will be full of errors. Examples:- Speedometer is used to measure the speed of the vehicles. The measuring tape is used to measure the length of anything.

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For each step: 1 Mark
Following are the steps to measure the length of a curved line:
1) First of all, we have to take a thread.
2) Now place the thread along the path of the curved surface.
3) Mark the thread at the endpoint up to which you want to measure the length.
4) Place the thread on the scale starting from zero to the marked endpoint.
5) Measure this length withthe help of the scale.

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Solution: 2 Marks
The size of the foot varies from person to person. If footsteps of two persons are used to measure the length respectively, then the two distances may not be equal. Thus, a footstep is not a constant quantity. Hence, it cannot be used as a standard unit of length.

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Solution: 2 Marks
The International System of Units, universally known as the SI (from the French Systeme International d'Unites ) is necessary because lack of the standard unit of measurement would cause confusion and a waste of time in converting from one unit to another all the time.

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In Rectilinear or Linear motion, the object moves along a straight path.