Measurement of Length and Motion

  

EXERCISES ( QUESTION - ANSWERS)

A. Choose the correct answer.

1. (d)     2. (d)     3. (d)     4. (a)     5. (a)     6. (b)     7. (a)     8. (c)

B. Fill in the blanks.

1. measuring tape     2. metre     3. thread     4. vibratory     5. rolling

C. State True or False. Also correct the false statements.

1. True             

2. False, the SI unit of distance is metre.         

3. True

4. False, motion of a fly is an example of random motion.         

5. True

II. LOGIC BASED QUESTIONS

Short and Long Answer

Q. 1.  What kind of motion is executed by :

    (a)  an ant

    (b)  a car moving on the straight road

    (c)  pendulum of a clock

    (d)  potter’s wheel

    (e)  whirling a stone tied to a string

    (f)  a spin ball

Ans. (a) an ant—Random

    (b) a car moving on the straight road—Translatory

    (c) pendulum of a clock—Periodic/vibratory

    (d) potter’s wheel—Rotational

    (e) whirling a stone tied to a string—Circular

    (f) a spin ball—Rolling (translatory as well as rotatory)

Q. 2.    Why a handspan cannot be used universally as a unit of length ?

Ans. A handspan cannot be used universally as a unit of length because the length of a hand varies from person to person.

Q. 3. The given picture shows a non-circular track. Can motion on this track be periodic ? Give reason for your answer.

Ans. Yes, motion on this non-circular track can be periodic. Periodic motion refers to any motion that  repeats itself at regular intervals of time. If an object moves on this non-circular track and returns to  its starting point after completing one lap in the same period of time for each lap, the motion will be periodic. The shape of the track (whether circular or non-circular) does not affect periodicity as long as the motion satisfies the condition of repetition at regular time intervals.

Q.6. Arrange the following measurements in decreasing order : 1 mm, 1 km, 1 cm, 1 m

Ans. 1 km > 1 m > 1 cm  > 1 mm

Q.7.  Look at the picture of a man riding a bicycle. Suppose he is moving to the right side, mark at least three types of motions in the picture and name them.

Ans. (a) Rotational motion of the wheels about their axes.

        (b) Translatory motion of the wheels along the road.

        (c) Rolling motion.

III. HIGHER ORDER THINKING SKILLS

Q. 1.    Why are the co-passengers in a train appear to be stationary, while the trees outside appear to move to a passenger sitting in the train ?

Ans. This happens because of relative motion. The co-passengers inside the train are moving with the same speed and in the same direction as the train. Since both you and they are moving together, there is no relative motion between you, so they appear stationary. 

While the trees outside are actually stationary on the ground, but the train (and you) are moving. Because of this relative motion between you and the outside objects, they appear to move backward.

Q. 2. A turning screw undergoes two kinds of motion at the same time. Identify the two kinds of motion.

Ans. When a screw is turned, it undergoes two types of motion at the same time :

        • Rotatory motion : The screw rotates around its own axis.

        • Translatory motion : The screw moves forward in a straight line.

Q.3. A student has to measure the length of his pencil. The zero mark on the scale is not clearly visible. How should he/she use the scale to get the correct length of the pencil ?

Ans. If the zero mark on a scale is not visible, one can measure the length of an object by placing it on a visible mark on the scale and subtracting the reading on that mark from the reading at the other end.