Ch-13 Questions 21 to 40

Chapter-13

Motion and Time

Sr NO.	QUESTION	ANSWER
21.	The metallic ball of the pendulum is called the ____ of the pendulum.	Bob.
22.	Give an example of a periodic or oscillatory motion	When the bob of the pendulum is released after taking it slightly to one side, it begins to move to and fro. The to and fro motion of a simple pendulum is an example of a periodic or an oscillatory motion.
23.	When we can conclude that pendulum completed one oscillation?	The pendulum is said to have completed one oscillation when its bob, starting from its mean position O, moves to A, to B and back to O. The pendulum also completes one oscillation when its bob moves from one extreme position A to the other extreme position B and comes back to A.
24.	What you mean by time period of a pendulum?	The time taken by the pendulum to complete one oscillation is called its time period.
25.	The time measured by _____ clocks is much more accurate than that by the clocks available earlier.	Quartz.
26.	The basic unit of time is a_____.	Second.
27.	The basic unit of time is a Second. Its symbol is ___.	s (small english alphabet letter 's')
28.	Larger units of time are _______ and_______.	Minutes (min), hours (h).
29.	What would be the basic unit of speed?	Since the speed is distance/time, the basic unit of speed is m/s. Of course, it could also be expressed in other units such as m/min or km/h. You must remember that the symbols of all units are written in singular. For example, we write 50 km and not 50 kms, or 8 cm and not 8 cms.
30.	How many seconds there are in a day and how many seconds in a year. Can you help him?	Seconds in a day: Number of seconds in I minutes=60 I hour is equal to 60 minutes. Number of seconds in one hour is sixty seconds sixty times. Number of seconds in one hour equal to 3600 seconds. One day is equal to 24 hours. One day is equal to 3600 seconds 24 times. Number of seconds in one day is equal to 86400 seconds. Seconds in a year: One year is equal to 365 and ¼ days(precisely). Number of seconds in one year 864400 seconds 365.25 times. Number of seconds in one year is 31557600 seconds. Number of seconds in one year is three crore fifteen lakh fifty seven thousand six hundred seconds.(31.55 million seconds).
31.	How many hours in a year?	One day is equal to 24 hours. One year is equal to 365 and ¼ days. Number of hours in one year is 24 hours 365.25 times. Number of hours in one year is 9131.25 hours.
32.	The pulse of a normal healthy adult at rest beats about 72 times in a minute that is about ____ times in 10 seconds.	12 (approximately).
33.	How time was measured when pendulum clocks were not available.	Sundials, water clocks and sand clocks were used before the discovery of pendulum.
34.	Rocket launching satellites into earth's orbit, often attain speeds up to _____ /s. 8 km.	8 km.
35.	A tortoise can move only with a speed of about ____/s.	8cm.
36.	How fast is the rocket compared with the tortoise?	Speed of a rocket is 8 km/s. Speed of a tortoise is 8cm/s Calculate how many centimeters are in one KM. One meter is equal to 100 centimeters. One kilometer is equal to 1000 meters. One kilometer is equal to 100 centimeters 1000 times. One kilometer is equal to 10000 centimeters. Compare the speed of a rocket with that of a tortoise. Eight kilometer is equal to 10000 centimetes 8 times. Eight kilometer is equal to 80000 centimeters. How many times is the speed of tortoise to the speed of a rocket: 80000 is devided by 8 which is equal to 10000 times. Speed of a rocket is ten thousand times the speed of a tortoise. In other words a rocket complete the distance in one second as that of the distance a tortoise complete in 10000 seconds.
37.	How can find the distance covered by an object in given time.	By multiplying speed by time we can calculate distance covered by an object in given time. Distance covered=Speed X Time.
38.	How can find the speed taken by an object in a given time.	Find the time an object would take to cover a distance while moving with a given speed. Timetaken = speed/distance
40.	What is the device to calculate the distance covered by a vehicle.	Odometer.