Short Question & Answers
Q1: What is rectilinear motion? Give an example.
Ans: When objects move along a straight line, such motion is called rectilinear motion. A sprinter in a 100m race moves along a straight track. This is an example of rectilinear motion.
Q2: Why can’t we use an angul (finger) or mutthi (fist) as standard unit of measurement of length?
Ans: We cannot use an angul (finger) or mutthi (fist) as standard unit of measurement of length because the sizes of body parts of different people are different. So it can create confusion.
Q3: What is the system of unit of measurement used all over the world now? What is that for length?
Ans: International system of units (SI Units) is the system of unit of measurement used all over the world now.SI unit for length is metre.
Q4: The height of a girl is 1.50 m. Express it into cm and mm.
Ans: The height of a girl in cm is 150 cm and in mm is 1500 mm.
Q5: What is the difference between motion of ceiling fan and motion of a pendulum?
Ans: Motion of ceiling fan is circular motion and motion of a pendulum is periodic motion.
Q6: What is circular motion? Give example.
Ans: When an object moves in a circular path, such motion is called circular motion. For example- Motion of a point marked on the blade of an electric fan is a circular motion.
Q7: Why can’t we use elastic tape to measure distances?
Ans: We can’t use elastic tape to measure distances because we will not know how much we stretched the tape during measurement. It will cause error.
Q8: What is periodic motion? Give example.
Ans: An object repeats its motion after some time; this type of motion is called periodic motion. For example- Motion of a pendulum is a periodic motion.
Q9: Arrange the following in increasing order:
1 km, 5 cm, 10 mm
Ans: 10 mm, 5 cm,1 km
Q10: The distance between ram’s house and Ravi’s house is 3000 m. Express it in km.
Ans: 1000 m =1km. Therefore 3000 m = 3km.
Q11: What is the difference between motion of a falling stone and motion of a stone tied to a tread and whirled with hand?
Ans: The motion of a falling stone is rectilinear motion and motion of a stone tied to a tread and whirled with hand is circular motion.
Q12: A thread is 2 m long. Express its length in cm and mm.
Ans: 200 cm and 2000 mm
Q13: How can we measure a curved line?
Ans: We can measure the length of a curved line by using a thread. Measure the length between the beginning and final mark on the thread.
Q14: Reena is 10 cm taller than shikha. Height of shikha is 160 cm. What is height of Reena?
Ans: Height of Reena is 160+10= 170 cm.
Q15: Arrange the following in decreasing order:
1 km, 1 mm, 1 cm, 1 m
Ans: 1 km, 1 m, 1 cm, 1 mm.
Q16: What is the difference between rectilinear and circular motion?
Ans: 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.
Q17: Name some units of length?
Ans: Units of length are kilometres, metres, centimetres, millimetres etc.
Q18: What is the difference between kilometres and kilogram?
Ans: Kilogram is the unit of weight whereas a kilometre is unit of length.
Q19: Fill in the blanks:
(a) Motion of wheel of car is ___________ motion.
(b) Motion of strings of guitar is __________ motion.
(c) 3 km is equal to _____m.
(d) Motion of a pendulum is __________ motion.
Ans:
(a) circular
(b) Periodic
(c) 3000
(d) Periodic.
Q20: What is the difference between rectilinear and circular motion?
Ans: 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.
Q21: While measuring the knitting needle’s length, the reading of the scale at one end is 3.0 cm and at the other end is 33.1 cm. What is the length of the needle?
Ans: Length of the needle = 33.1 cm – 3.0 cm = 30.1 cm.
Q22: Four children measured the length of a table which was found to be about 2 metres. Each of them used different techniques to measure it.
(i) Sam measured it with a half-metre-long thread.
(ii) Ana measured it with a 15 cm scale from her geometry box.
(iii) Reena measured it using her hand span.
(iv) Salim measured it using a 5 m long measuring tape.
Which one of them would get the most accurate length? Give a reason for your answer.
Ans: Salim would measure the length with the greatest accuracy because he uses a measuring tape that is 5 m long, which is longer than the table. As a result, he can quickly and accurately measure the length of the table. In contrast, the other situations include more measurements, which increases the possibility of inaccuracy. Sam can only have lengths that are precise multiples of 0.5 metres measured.
Q23: What is meant by rectilinear motion? Give two examples.
Ans: Any motion in which objects move in a straight line is known as rectilinear motion.
Examples: Motion of any vehicle on a straight road, a moving train
Q24: What type of motion do the following objects exhibit?
(a) the sewing machine’s needle
(b) the galloping of a horse
(c) the blades of an electric fan
(d) the movements of a mosquito
(e) wheels of a moving car.
(f) the smoke from a lighted dhoopbatti
Ans:
(a) The sewing machine’s needle: Periodic motion.
(b) The galloping of a horse: Linear motion.
(c) the blade of an electric fan: Circular motion.
(d) Movement of a mosquito: Random motion.
(e) Wheels of moving car: Linear motion and Rotational motion.
(f) The smoke from a lighted dhoopbatti: Random motion.
Q25: Why couldn’t you measure the distance using an elastic measuring tape? What problems might you have when telling someone about a distance you measured with elastic tape?
Ans: The distance between two points is incorrectly measured using an elastic measuring tape.
Reasons:
(i)The elastic tape length fluctuates and is influenced by the force used to stretch it.
(ii) Even when measured by the same individual using the same elastic tape, measurements could differ by two or three readings.
(iii) The measurement will also differ if various people measure the same distance.
Q26: While travelling on a train, it appears that the trees near the track are moving, whereas the co-passengers appear to be stationary. Explain the reason.
Ans: The trees appear to be moving in the opposite direction when we look out the window of a moving train because they are shifting their position with respect to us. Co-passengers, on the other hand, appear to be stationary because their location in relation to us is not moving.
Q27: Why can’t a pace or a footstep be used as a standard unit of length?
Ans: A pace or a footstep can not be used as a standard unit of length because the pace or footstep of each and every person is not equal.
Q28: Three students determined the length of a corridor and reported their measurements. The values of their measurements were different.
What could be the reason for the difference in their measurements? (Mention any three)
Ans: They could differ in measurement for a variety of reasons, including
(i) There were many measuring tools employed.
(ii) Various measuring tools may have varying minimum lengths that can be measured.
(iii) The measurement may not be along the shortest length in all three instances.
(iv) It can be difficult to get to the end of the corridor.
(v) The measuring tools may be faulty (not standardised).
Long Question & Answers
Q1: What are different types of motion? Explain with example.
Ans: When objects move along a straight line such motion is called rectilinear motion. A sprinter in 100m race move along a straight track. This is an example of rectilinear motion. When an object moves in a circular path, such motion is called circular motion. For example- Motion of a point marked on the blade of an electric fan is a circular motion. An object repeats its motion after some time; this type of motion is called periodic motion. For example- Motion of a pendulum is a periodic motion.
Q2: How can you measure the length of a curved line?
Ans: The length of a curved line is measured using a thread or a divider. Take a long thread. Let one end of the thread be placed at one end of the branch of the plant. Run the thread at straight distances on the branch from A to B, then from B to C and so on till the length of thread runs on full length of the branch. Shifting your hand from the previous to the next position, mark on the thread when it reaches the end of the branch. The length of the thread you have run is equal to length of the branch. Place this thread on the scale with its one end at ‘0’. Take the reading on the other end. You will get the length of the curved branch of the plant.
Q3: Four children measured the length of a table which was about 2 m. Each of them used different ways to measure it.
(i) Sam measured it with a half metre long thread.
(ii) Gurmeet measured it with a 15 cm scale.
(iii) Reena measured it using her handspan.
(iv) Salim measured it using a 5 m long measuring tape.
Which one of them would get the most accurate length? Give reason for your answer.
Ans: Salim would get the most accurate length. The reason is that in this case the length of the table can be measured in one go because the measuring tape is longer than the table. In the other cases the chance of making an error is higher due to multiple measurements. In case of Sam, he can only measure the lengths which are exact multiples of a half metre.
Q4: Three students measured the length of a corridor and reported their measurements. The values of their measurements were different. What could be the reason for difference in their measurements? (Mention any three.)
Ans: Some of the reasons for difference in their measurements could be:
- Different measuring devices were used.
- The smallest length that could be measured by different devices may be different.
- Measurement may not be along the shortest length in all three cases.
- The end of the corridor may not be easily accessible.
- The measuring devices may be faulty (not standardised).
Q5: Boojho was riding in his bicycle along a straight road. He classified the motion of various parts of the bicycle as (i) rectilinear motion, (ii) circular motion and (iii) both rectilinear as well as circular motion. Can you list one part of the bicycle for each type of motion? Support your answer with reason.
Ans: (i) Handle bar or seat because handle or seat is moving along a straight road, not rolling.
(ii) Pedal because it is rolling around a fixed centre by the foot.
(iii) Wheel because it is rolling and also moving along a straight road.
Q6: What are different types of motion? Explain with example.
Ans: When objects move along a straight line such motion is called rectilinear motion. A sprinter in 100m race move along a straight track. This is an example of rectilinear motion. When an object moves in a circular path, such motion is called circular motion. For example- Motion of a point marked on the blade of an electric fan is a circular motion. An object repeats its motion after some time; this type of motion is called periodic motion. For example- Motion of a pendulum is a periodic motion
Q7: Why do we need standard unit for measurement?
Ans: We need standard unit for measurement to make our judgement more reliable and accurate. For proper dealing, measurement should be same for everybody. Thus there should be uniformity in measurement. For the sake of uniformity we need a common set of units of measurement, which are called standard units. Nowadays SI units are used in science and technology almost universally.
Q8: What type of motion do the following objects have?
(a) the galloping of a horse
(b) the needle of a sewing machine
(c) the movements of a mosquito
(d) the blades of an electric fan
(e) the smoke from a lighted dhoopbatti
(f) wheels of moving car.
Ans:
(a) The galloping of a horse: Linear motion.
(b) The needle of a sewing machine: Periodic motion.
(c) Movement of a mosquito: Random motion.
(d) Blade of an electric fan: Circular motion.
(e) The smoke from a lighted dhoopbatti: Random motion.
(f) Wheels of moving car: Linear motion and Rotational motion.
Q9: Give two examples for each of the following motions:
(i) Linear motion
(ii) Spinning motion
(iii) Oscillatory motion
(iv) Periodic motion
(v) Vibrational motion
(vi) Circular motion
(vii) Random motion
Ans:
(i) Linear motion: (a) Rolling of ball on ground, (b) Moving of bicycle on road,
(ii) Spinning motion: (a) Rotating fan, (b) Wheel of sewing machine.
(iii) Oscillatory motion: (a) Pendulum of clock, (b) Motion of a child on a swing,
(iv) Periodic motion: (a) Pendulum of clock, (b) Motion of a swing, heartbeat.
(v) Vibrational motion: (a) String of a guitar, (b) Surface of drums.
(vi) Circular motion: (a) Rotation of fan, (b) Bicycle wheel.
(vii) Random motion: (a) Motion of football players, (b) Movement of mosquito.
Q10: How are the motions of a wheel of a moving bicycle and a mark on the blade of a moving electric fan different? Explain.
Ans: The wheel of a moving bicycle depicts circular as well as rectilinear motion whereas a blade of a moving electric fan shows only circular motion.
