Motion and Measurement of distances

Q20. Why can't hand span and cubit be used as standard units?

Ans. Hand span and cubit cannot be used as standard units because everyone's body parts could be of slightly different sizes which cause confusion in measurement.

Q21. Why we should not use an elastic tape for measuring the length?

Ans. We should not use an elastic tape for measuring the length because elastic measuring tape is stretchable and the length of the tape may change on stretching. Thus, an elastic tape gives wrong measurement.

Q22. State the 3 precautions which should be taken while using a metre scale to measure length.

Ans. In taking measurement of a length, we need to take care of the following:

      i.     Place the scale in contact with the object along its length.

      ii.    Avoid taking measurements using broken scale.  

      iii.  Eye must be exactly in front of the point where the measurement is to be taken.

Q23. How people travelled from one place to another in earlier times before the discovery of wheel?

Ans.  Long ago people used to move only on foot and carry goods on their back or using animals. For transport along water routes, boats were used from ancient times.

Q24. Write the steps to measure the length of objects using measuring tape.

Ans. Steps to measure the length of objects using measuring tape:

      i.     Place the measuring tape in contact with the object along its length.

      ii.    Take the measurements from the zero mark of the measuring tape.

      iii.  Note the reading at the other end of the object.

      iv.  This gives the measure of the length of the object.

Q25. Write the unit for measuring the following:

                         i.        Distance between Noida and Gurugram - Kilometre

                        ii.        Thickness of compact disc (CD) - Millimetre

                       iii.        Length of a sharpener - Centimetre

                       iv.        Length of a tie – Centimetre

                       v.        Length of a sari – Metre

Q26. Name the device used to measure the following:

                       i.        Size of shoulder – Measuring tape

                      ii.        Size of waist – Measuring tape

                     iii.        Height of a pole – Measuring tape

                     iv.        Weight of an object – Weighing balance

                      v.        Fabric for a dress – Measuring tape or Metre scale

                     vi.        Circum ference of a round platform – A long thread or Measuring tape

Q27. “Pace or footstep cannot be used as standard unit of length”. Comment

Ans. The size of foot varies from one person to another. Length measured by footsteps of two different persons may not be equal. Thus foot step is not a fixed quantity as it differs from person to person. Hence, it cannot be used as standard unit of length.

Q28. Distance between Ayush’s home and his office is 14.5 km. How much time will he take to reach his workplace if he is travelling by a car with a speed of 30,000 m/hr.?

Ans. 14.5 km = 14.5 x 1000 = 14500m

Car covers 30,000m in 1 hr.

Car covers 1m in 1/30,000 hr.

Car covers 14500m in 1/30,000 x 14500 = 0.4833 hrs.

= 0.4833 x 60 = 29 minutes

Q29. How invention of wheel made a great change in modes of transport?

Ans. The invention of wheel brought in a great change in the modes of transport. People employed carts and chariots to travel from one place to another. It made the transportation of goods and people much easier. Modern means of transport such as cars, buses, trains and airplanes allow us to travel faster than those used in earlier times.