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CBSE Questions for Class 7 Physics Motion And Time Quiz 3 - MCQExams.com
CBSE
Class 7 Physics
Motion And Time
Quiz 3
The quantity which tells the distance an object travels in a certain time is called -
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acceleration
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speed
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velocity
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none of these
Explanation
The quantity which tells the distance an object travels in a certain time is called speed.
$$Speed = \dfrac{Distance}{Time}$$
Speed can be positive, zero or negative. True or false
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True
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False
Explanation
Speed is a scalar quantity and only have magnitude which cannot be negative. It can either be positive or zero.
A boy cycles a distance of 640 m in 2 minutes and 40 seconds. What is the speed of the cycle?
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4 m/s
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8 m/s
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12 m/s
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16 m/s
Explanation
Distance covered = 640 m
Time taken = 2 min 40 sec
= $$2$$ $$\displaystyle \times 60 + 40 = 160s$$ (because 1 minute =60seconds)
$$\displaystyle \therefore Speed = \frac{Distance}{Time}= \frac{640}{160}=4m/s$$
Which of the following formulae is correct?
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Speed=Distance$$\times $$time
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Speed=$$\frac { Time }{ Distance } $$
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Speed=$$\frac { 1 }{ Distance\times time } $$
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Speed=$$\frac { distance }{ time } $$
Explanation
Speed of an object is defined as distance moved per unit time.It denotes how fast or how slow the object is moving.It is given by
$$Speed=\dfrac{Distance}{time}$$
Right sequence in increasing magnitude is:
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decade, second, week, nanosecond
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nanosecond, week, second, decade
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nanosecond, second, week, decade
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nanosecond, decade, second, week
Explanation
$$1 ns = 10^{-9} s$$
$$1 week = $$ 7 $$days$$ = $$604800s$$
$$1 decade = 10 yrs$$ = $$3.17\times 10^{-9}s$$
So correct order is option C.
A century has:
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$$100\ years$$
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$$100\ months$$
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$$100\ seconds$$
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$$100\ weeks$$
Explanation
$$1\ century = 100\ years$$
A century has 100 years.
For measuring time in sports events like sprinting, $$mili second (ms)$$ is a commonly used unit of time. $$1ms=?$$
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$$10^{-12}s$$
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$$10^{-9}s$$
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$$10^{-3}s$$
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None of these
Explanation
$$1\ ms=\dfrac{1}{1000} s=10^{-3}s$$
Which of the following methods of measurement of time is suitable for a race?
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Stop watch
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Wall clock
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Simple pendulum
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Reflection of an object by sun rays
Explanation
$$Answer:-$$ A
Stop watch is used because of its precise measurement since its least count is less so able to measure fractions of a second which is required in a race because sometimes time taken by two contestants differ only by a fraction of a second so stopwatch helps in determining the winner.
How many seconds are there in a week?
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60480
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604800
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6048000
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6048
Explanation
$$1 week = 7 days$$
$$= 7 days \times 24 hrs/day \times 60 min/hr \times 60 sec/min$$
$$= 604800 s$$
Measurement of time can be done with the help of a:
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Meter scale
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Pulley
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Simple pendulum
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Speedometer
Explanation
$$Answer:-$$C
A
pendulum
is a weight suspended from a pivot
so that it can swing freely.
When a pendulum is displaced sideways from its resting, equilibrium position
, it is subject to a restoring force
due to gravity
that will accelerate it back toward the equilibrium position. When released, the restoring force combined with the pendulum's mass causes it to oscillate
about the equilibrium position, swinging back and forth. The time for one complete cycle, a left swing and a right swing, is called the period
. The period depends on the length of the pendulum .
This time period when known can be used to measure time.
The diagram shows the pattern of the oil dripping on the road, at a constant rate from a moving car.
Which of the following statements is correct?
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The car moves initially with a constant speed and then slows down
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The car accelerates initially and then moves with a constant speed
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The car starts from rest and keeps accelerating
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The car moves with a constant speed all along
Explanation
Initially, the drops are at a uniform separation.The rate of dripping being constant, the motion, then, is with a constant speed.
Later on, the spacing between the drops keeps decreasing.This means, within same time interval, the car covers lesser distance as the time progresses.
So, later, the car slows down.
The time taken by the earth to complete one rotation about is own axis is called
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Solar day
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Mean solar day
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1 hour
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None
Explanation
Solar day is defined as the time taken by the earth to complete one rotation about its own axis.
A car travels first $$60 \ km$$ of a distance in $$1 \ hr$$, next $$70 \ km$$ of the distance in next hour and remaining $$20 \ km$$ distance in final hour. Then, its motion is:
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uniform motion
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non-uniform motion
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either uniform or non-uniform motion
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neither uniform nor non-uniform motion
Explanation
During first hour, speed = $$\dfrac{60}{1} \ km/h = 60 \ km/hr$$
During second hour, speed = $$\dfrac{70}{1} \ km/h = 70 \ km/hr$$
During third hour, speed = $$\dfrac{20}{1} \ km/h = 20 \ km/hr$$
So, the car travels different distances in equal time intervals.
This is an example of non-uniform motion.
Which of the following is/are unit of time
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Solar day
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Hour
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Mean solar day
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All
Explanation
All are units of time. The time taken by the earth to complete one rotation about its own axis is called solar day.
A person has two hourglasses, one of $$30\ seconds$$ and the other of $$1\ minute$$. Which of the following time intervals can he not measure?
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$$30\ seconds$$
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$$60\ seconds$$
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$$50\ seconds$$
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$$90\ seconds$$
Explanation
A person has two hourglasses, one of $$30\ seconds$$ and the other of $$1\ minute$$.
$$1\ minute=60\ seconds$$
$$\text{H.C.F. of}\ 30\ seconds$$ and $$60\ seconds=30\ seconds$$
He can only measure time intervals of $$30,\ 60,\ and 90\ seconds$$.
But he cannot measure the time interval of $$50\ seconds$$.
Which of the following clocks is most accurate?
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Simple pendulum
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Stop watch
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Caesium clock
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Hourglass
Explanation
Caesium clocks are the most accurate commercially produced time and frequency standards, and serve as the primary standard
for the definition of the second
in SI system.
Hence,
Caesium clock is most accurate clock
Option C is correct.
Which of the following is used as measuring time?
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Sand glass
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Computer
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Laptop
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Mobie
Explanation
An hourglass (or sandglass, sand timer, sand clock or egg timer) is a device used to measure the passage of time. It comprises two glass bulbs connected vertically by a narrow neck that allows a regulated flow of a substance (historically sand) from the upper bulb to the lower one.
When will a body have zero speed?
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When a body has uniform acceleration
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When a body has non-uniform acceleration
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When a body is at rest
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When a body is under motion
Explanation
The distance travelled by a body per unit time is known as speed.
$$speed=\dfrac{distance}{time}$$
A body has zero speed when it has zero distance covered in an interval of time and hence the body is at rest.
Which of the following is not used to measure time?
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Computer
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Mobile
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Wrist watch
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Candle clock
Explanation
The candle clock was used to measure time in ancient times whereas nowadays, computers, mobile,s, and wristwatches are used to measure time.
Which of the following is required to facilitate the measurement of time?
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A wave with high energy
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A periodic event
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A device calibrated to measure time
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Both B and C
Explanation
In order to facilitate the measurement of time, a periodic event is required along with a device to calibrate the measured time.
Thus option D is correct.
$$4.15\ p.m$$. in $$12$$ hour system is written as _____ in $$24$$ hour clock system.
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$$11 hours\ 46 minutes$$
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$$4 hours\ 15 minutes$$
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$$22 hours\ 15 minutes$$
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$$16 hours\ 15 minutes$$
Explanation
In $$24$$ hour clock system , $$4.15\ p.m.$$ will be written as
$$12+4.15=12 hrs+ 4 hrs+ 15 minutes= 16hours\ 15 minutes$$
An hour glass is also known as :
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Sand glass
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Sand timer
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Sand clock
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None of the above
Explanation
An hour glass is also known as sand glass, sand timer and sand clock.
How many days are present between the years 2005 and 2008 including these years?
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1461
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1460
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730
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731
Explanation
We know that, in one year, there are $$365$$ days. Out of the year $$2005, 2006, 2007$$ and $$2008$$, the year $$2008$$ is a leap year which has $$366$$ days.
So, total number of days $$ = 365+365+365+366 = 1461$$ days
The meter that is used to measure the distance moved by the vehicle is known as _____. Fill in the blank.
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Speedometer
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Odometer
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Chronometer
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Ammeter
Explanation
Odometer is an instrument used in the vehicle to measure the distance cover by it.
Speedometer drive is usually taken from :
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Dynamo
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Fan belt
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Flywheel
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Front wheel
Explanation
Speedometer drive is usually taken from front wheel.
The meter that is used to measure speed of a vehicle is :
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Speedometer
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Odometer
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Anemometer
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Thermometer
Explanation
Speedometer is the device used in vehicle to measure speed of that vehicle.
What is the use of speedometer in a vehicle?
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Displays the mileage of the vehicle
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Displays the instantaneous distance of a vehicle
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Displays the instantaneous speed of a vehicle
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All of the above
Explanation
Speedometer in the vehicle shows the instantaneous speed of the vehicle.
Among the following which was used to measure time in ancient time?
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Alarm clock
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Chronometer
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Sundial
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All of the above
Explanation
In the ancient time, sundial was used to measure time.
Identify which of the following is/are the time measuring device(s)?
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0%
0%
0%
Explanation
Time can be measured by sand glass, stop watch and digital clock but time cannot be measured by using meter scale.
Thus option A, B and C are correct options.
A speedometer typically has a threshold of about 15 km/hr. If the car starts from rest and accelerates, the speedometer will :
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Start reading from the moment the car starts
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Start reading when the speed reaches 15 km/hr
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Start reading when the speed reaches 30 km/hr
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None of these
Explanation
Threshold of the speedometer represents the minimum speed of the vehicle by which it must be moving to display the instantaneous speed of the vehicle. Thus, $$15 \ km/hr$$ threshold of the speedometer means that it starts reading the speed of the vehicle once the speed reaches $$15 \ km/hr.$$
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