Ans: a. The scale that you are using to measure the object must be greater than the length of the object.
b. The eye should be placed just above the points that you are reading otherwise there will be error due to parallax.
c. If the zero mark of the scale is damaged or edge of scale is not smooth, then start measuring from another mark.
2. Name two devices used to measure length.
Ans: The two devices that can be used to measure length are:- Metre scale ad Screw gauge.
3. Describe the correct method of measurement of length.
Ans: (i) we must choose a suitable device for measuring the length of an object, like measuring scale
(ii) we should place the scale in contact with an object along its length and align the zero mark of the scale with the starting position of the object.
(iii) While taking the reading, eye must be placed vertically above the point where the measurements have to be taken; otherwise there will be an error in the reading which is taken due to parallex.
(iv) if the zero mark on the scale is damaged, then start the measurement from another mark.
4. Circle odd one
(a)Table; fan; falling stone; Parked car
(b)Bee ; butterfly; Grazing Cow; Sleepy Donkey
(c)Pendulum; Earth revolving around the Sun; Moon revolving around the earth; Bee revolving on flowers
(d)Moving fan; merry go round; A bus moving on road; a stone moving along circular track
Ans: (a) falling stone (b) Sleepy Donkey (c) Bee revolving on flowers (d) A bus moving on road
5.Fill in the blanks
1.One meter is --------------cm
2.one centimeter is -----------------mm
3. Four km is ---------m
4. The motion of moving bicycle is ----------------
5. The motion of drill machine is ----------
6. Motion of child on swing -------------
7. The motion of a top is ----------
Ans: 1. 100 2. 10 3. 4000 4. Rectilinear 5. rotatory 6. oscillatory
6. Say true or false
(a)Rectilinear and curvilinear cannot happen at the same time
(b)Rupa can move in rectilinear and rotationary motion at the same time
(c)A child on swing has only circular motion
(d) Periodic motion is always rectilinear
(e) A foot step is used as a standard unit of length.
Ans: (a)False (b)True (c) False (d) False (e)False
1. Can an object be in motion and rest simultaneously for different observer? Give an example and consequence?
Ans: Yes. A person driving a car is in rest with respect to other person in car but in motion with respect to a person standing road side. Tate of motion and rest depend on the observer or a fix point called reference point.
2. Can a body be in translational and rotational motion? Give some examples
Ans: yes, combination of translation and rotation is rolling motion like the motion of the wheel , the motion of the earth, drilling.
3. Why do we need standard unit of measurements for a quantity?
Ans: The unit used like hand span ,foot, cubit differ from person to person or even in different countries so for a uniform measurement we need standard unit of measurements.
4. Is it correct to say all periodic motion are oscillatory motion and all oscillatory motion are periodic. Give reason for answer?
Ans: In oscillatory motion body repeat its action in equal interval of time so, all periodic motion are oscillatory motion and vice versa. For example motion of swing, pendulum, motion of earth on its axis.
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