A. FILL IN THE BLANKS.
1. The standard unit of mass is the ______.
Ans: kilogram
2. While sitting in a moving bus, we are in ______ with respect to the surroundings.
Ans: Motion (with respect to the outside surroundings)
Rest (with respect to the inside surroundings)
3. A moving car, going on a narrow straight road, is having a (nearly) ______ motion.
Ans: rectilinear
4. The motion, of the needle of a sewing machine, is an example of an ______ motion.
Ans: rectilinear
5. The motion of the earth, around the sun, is _____ in nature.
Ans: periodic
B. WRITE TRUE OR FALSE FOR THE FOLLOWING STATEMENTS.
1. Measurement is needed to make correct decisions. True
2. A metre scale can be used for measuring the length of a playground. False
3. The motion of the moon, around the earth, is a rectilinear motion. False
4. The motion, of the pedal of a bicycle, is a circular motion. True
5. The motion, of a giant wheel, is a rotatory motion. True
6. When we draw water from a well, we are pushing at the rope. False
C. TICK THE CORRECT OPTION.
1. The standard unit of length is the-
(a) metre (b) millimetre (c) kilometre (d) centimetre
Ans: metre
2. The standard unit of time is the-
(a) second (b) day (c) year (d) minute
Ans: second
3. The motion, of the tip of a pen, while writing, is a/an-
(a) Rectilinear motion (c) Oscillatory motion
(b) Curvilinear motion (d) Rotatory motion
Ans: curvilinear
4. Which of the following four ‘motions’ is different from the other three?
(a) The moving blades of a fan (b) a spinning top
(c) A potter’s wheel (d) a fruit falling from a tree
Ans: a fruit falling from a tree
5. The motion of a swinging pendulum is a/an-
(a) Curvilinear motion
(b) Rotatory motion
(c) Oscillatory motion
(d) Rectilinear motion
Ans: oscillatory motion
D. ANSWER THE FOLLOWING QUESTIONS IN BRIEF.
1. How does measurement help us in our day-to-day life?
Ans: Measurement helps us to make correct decisions.
2. Which type of watch is used to measure time intervals in a ‘200 metre race’?
Ans: Stop watch is used to measure time intervals in a ‘200 metre race’.
3. When do we consider an object to be in motion?
Ans: If the object changes its position with respect to time and with reference to the reference point, then the object is said to be in motion.
4. Name three different types of motions and give one example of each.
Ans: i) Rotational motion- The earth rotates around its own axis
ii) Revolution: The moon revolves around the earth.
iii) Rectilinear motion: Light travels in a straight line
5. State the difference between a ‘periodic’ and a ‘non-periodic’ motion.
Ans: PERIODIC MOTION: A motion is said to be periodic if it repeats itself after a regular time interval.
NON-PERIODIC MOTION: A motion is said to be non-periodic if it, (i) either does not repeat itself or (ii) does the repetitions in a random irregular manner.
E. ANSWER THE FOLLOWING QUESTIONS.
1. Why does a measurement need both a ‘number’ and a ‘unit’ for its complete specification?
Ans: i) We need both the ‘number’ and a ‘unit’ to express the measurement in a proper and complete way.
ii) A comparison between the unknown quantity (number) with some known fixed quantity (unit) gives us the required measurement.
iii) The number tells us as to how many times does the unit get contained in the physical quantity to be measured.
2. Why is a foot step, or a hand span, not used as a standard unit of length?
Ans: Length of a foot step or a hand span differs from person to person. Their length is not fixed. Thus, they cannot give us the accurate measurement. So, these are not used as a standard unit of length.
3. Radha was performing an experiment in the Science Laboratory. The metre scale, that she was using to measure the length of a string, was worn out between its 1 cm and its 2 cm marks, due to overuse.
(a) She measures the length of a string by keeping its one end at the 3.0 cm mark. If the other end of the string ‘reads’ 92.8 cm, find the length of the string.
Ans: Length of the string = final reading – initial reading
Therefore, the length of the string = 92.8 cm – 3.0 cm = 89.8 cm
(b) Write the precautions, to be followed, when a metre scale is being used for measuring a given length.
Ans: The following precautions are to be followed when a metre scale is being used for measuring:
i) Place the scale in such a way that the edge of the scale should be parallel to the length to be measured, or should coincide with it.
ii) The scale should be kept exactly along the length to be measured.
iii) The zero mark of the scale should coincide with one end of the length to be measured.
iv) Keep the vertically above the end point, and in line with the reading to be taken.
v) Do not use the worn out portion of the metre scale for measuring length.
4. Explain the difference between ‘rest’ and ‘motion’. Give two examples of each.
Ans: i) REST: An object is at rest if it does not change its position with respect to its immediate surroundings. For example, the walls of a room.
ii) MOTION: An object is in motion if it keeps on changing its position with respect to its immediate surroundings For example, the blades of a moving fan.
5. Distinguish between:
(a) Rectilinear and Curvilinear motion
(b) Rotation and Revolution
Give one example of each from our daily life.
Ans: (a) RECTILINEAR MOTION: An object is said to have a rectilinear motion if it changes its position all along a straight line path. Example, Motion a vehicle on a straight path.
CURVILINEAR MOTION: When an object moves from one position to another, along a curved line, the object is said to have a curvilinear motion. Example, the motion of the tip of a pen while writing.
(b) ROTATION: An object is said to have rotational motion if it moves around its own axis repetitively. Example, the motion of a potter’s wheel.
REVOLUTION: The repetitive motion of an object around another central object, following a circular (or nearly circular) path, is said to be revolutionary. Example, the motion of hands of a clock
6. Define the following types of motion:
(a) Rectilinear motion
(b) Circular motion
Give one example of each of these two types of motion.
Ans: a) RECTILINEAR MOTION: An object is said to have a rectilinear motion if it changes its position all along a straight line path. Example, Motion a vehicle on a straight path.
b) CIRCULAR MOTION: When an object moves around another object, as a whole repetitively, in a perfectly circular path, its motion is said to be circular motion. Example, When a ball tied to a string and whirled round and round.
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