Question 4 SHORT ANSWER TYPE QUESTION
(i)Arrange the following lengths in descending order.
1 millimeter; 1kilometer; 1 meter; 1 decameter ;1 decimeter
(ii)Define rectilinear motion
(iii) Ramesh’s mom asked him to go get paneer from the market. The market is 1550 m from his home. Express this distance into km
(iv)Define periodic motion.
(v)Which measuring device can be used to measure the girth of a tree? Why SI unit of measurement came into existence? Answers
(i)1 kilometer > 1 decameter > 1 meter > 1 decimeter> 1 millimeter
(ii)When an object moves along a straight line it is called rectilinear motion.
(iii)We know that 1 km = 1000 m
Or, 1000 m = 1 km
Or, 1m = 1/1000 Km
Thus, 1550 m = (1/1000) X 1550 = 1.55 Km
Therefore, distance between Ramesh’s home and the market in km = 1.55 km
(iv)The motion which repeats itself after a fixed interval of time is called periodic Motion. For example, earth moving in the orbit around the sun.
To overcome the inconsistencies of measurement, people felt the need for standard units of measurement
Question 5 VERY SHORT ANSWER TYPE QUESTION
(i)Name the SI unit of length and mass.
(ii)How many kilograms are there in 2 metric tons?
(iii)Give two examples of periodic motion.
(iv)What is estimation?
(v)When is a body said to be at rest? Answers
(i)SI unit of length – meter
SI unit of mass – kilogram
(iii)(a) Needle of a sewing machine
(iv)Ans. the ability to guess the amount of anything without actual measurement is called estimation
(v)an object that does not change its place or position with time, relative to its surroundings is said to be at rest.
What kind[s] of motion is shown by the following?
Kite flying in the sky ___________
Motion of a bicycle ___________
A honeybee buzzing around in the park ___________.
How can we measure a curved line? Answers
A curved line or surface cannot be measured by a straight scale, a measuring tape or thread must be used instead. To measure a curved line using a thread, follow the below steps:
Tie a knot at one end of the thread.
Place the thread at the beginning of the line and try to measure a small initial portion of the line which is relatively straight.
Place your thumb at the other end of the measured portion and measure next straighter portion.
Repeat the above step till the end of line is reached. Make a knot at the end of the line.
Now, straighten the thread and measure the length of the two knots on a scale.
Define position of an object and reference point? Answers
Position: Position is the location of the object.
Reference point: It is the point from which the location of object is measured. It is often called as origin.
Why can a pace or a footstep not be used as a standard unit of length? Answers
Because the size of pace or footstep of different people are different so the lengths measured by two different persons using their footsteps will not be the same. Due to this reason pace or a footstep cannot be used as a standard unit of length.
Write the similarities and difference between the motion of a bicycle and a ceiling fan that has been switched on. Answers
The wheel of a bicycle and a ceiling fan moves in a rotational motion around a fixed axis.
Bicycle change its position but a ceiling fan does not change its position.
Bicycle can execute rectilinear motion but ceiling fan does not execute rectilinear motion.
An object that does not change its positions with time is said to be at rest.
An object that changes its positions with time is said to be in motion.
Why can’t you use an elastic tape to measure a distance? Answers
We should not use an elastic tape to measure the distance as it will give false reading when stretched or pulled. A measuring tape must be made up of such a material which does not expands on pulling force like wood, iron, hard plastic.
Name the two parts which must be mentioned to express the value of a measurement. Answers
Quantity express in numerical. (1, 100, 5, .06 etc)
Unit (meter, liter, second, etc.)
Define Uniform and Non-uniform Motion. Answers
Uniform motion: It is a motion, in which equal distance is covered in equal time intervals.
Non - uniform motion: It is a motion, in which unequal distance is covered in equal intervals of time.
What does the path of an object look like when it is in uniform motion? Answers
In the case of uniform motion the path of an object will look like a straight line
Four friends measured the length of a field. All of them got different result. List minimum three reasons for such discrepancy? Answers
The various reasons may be:
1. Faulty or damaged measuring tape.
2. Improper technique of using the tape
3. Using nonstandard unit of measurement.
Can an object be in motion and rest simultaneously for different observer? Give an example and consequence? Answers
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
Is it correct to say all periodic motion are oscillatory motion and all oscillatory motion are periodic. Give reason for answer? Answers
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
LONG ANSWER TYPE QUESTION.
The scouts were asked by the teacher to run around a square field in the school for 7 min. In the first 30 seconds they covered only one side the field which is 100 m.
(a)7 min = 420 seconds
The distance covered in 30 s is 100m
The distance covered in 1 s is 100m/30
The distance covered in 420 s is 100x420/30=1400m
The perimeter of the field = 4x 100m
So, after running every 400 m the net displacement is zero.
After running 1400 m, if they started from point A then they will be at point C after running 7.5 times around the field.
So, the shortest distance between A & C = √ (AD2 + DC2)
= √(1002 + 1002)
= 100 √2 m
So, the displacement will be 100√2 m
a. Differentiate between distance and displacement.
b. Can the displacement of an object be zero but positive distance?
c. can the displacement of an object be more than the distance travelled by it. Answers
a. Distance is a quantity that refers to "how much ground an object has covered" during its motion from one point to the other. Or, the total length travelled from one point to another.
Displacement is the shortest distance travelled from one point to another.
b. Yes, it is possible to have a positive distance yet zero displacement. When the object returns back to its origin after travelling, then the displacement is zero.
c. No, it is not possible. Displacement can never be more than distance,by definition displacement is the shortest distance between the point of origin and position of the object after travelling.
A. Give two examples for each of the following.
a. Circular motion
b. Random motion
c. Vibrational motion
B. How is rectilinear motion different from circular motion? Answers
Rotation of fan, motion of earth around the sun.
Flow of water in river, motion of dust particles.
String of a guitar when struck, beating the surface of drum.
B. When objects move along a straight line such motion is called rectilinear motion. Whereas when an object moves in a circular path, such motion is called circular motion
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