Class 7 Science Chapter 9 MCQ

The motion which repeats itself after regular intervals of time, is called periodic motion.

Here, all the statements are correct. Hence, your answer will be option [D].

As we know that, Speed = Distance/Time = 54 x 1000/90 x 60 =10 m/s

Here, all the statements are correct. Hence, your answer will be option [D].

The correct relationship is: S = 1 x D/ T Because, Speed = Distance travelled (D) / Time taken (T)

Here, all the statements are correct. Hence, your answer will be option [D].

Time taken for 20 oscillation = 32 s So, Time taken for 1 oscillation = 32 s / 20 = 1.6 s Thus, the time period of this pendulum is 1.6 seconds.

When the distance travelled is measured in kilometers and the time taken is measured in hours then the speed will come in the unit of kilometer per hour.

Here, all the statements are correct. Hence, your answer will be option [D].

Explanation: Here the speed has given to us in the units of meters per second and we have to convert it into the units of kilometers per hour. In order to this, we have to convert 10 meters into kilometers by dividing it by 1000. Since there are 60 x 60 seconds in 1 hour. We have also 10 by 60 x 60. We can convert the speed of 10 meter per second into kilometers per hour by dividing the speed of 10 by 1000 and multiplying it by 60 into 60. Now, Speed = 10 meter / seconds = 10 x 60 x 60 / 1000 = 36 km/h Thus, a speed of 10 m/s is equal to 36 km/h

Here, all the statements are correct. Hence, your answer will be option [D].

We know that, 1 kilometer = 1000 meter 320 km = 320000 meters 1 hour = 3600 seconds (60 x 60) Now, Speed = Distance travelled / Time taken = 320000 meter / 3600 = 3200/36 = 88.8 m/s

Different units of time are used depending on the need. For example, it is convenient to express your age in years rather than in days or hours. Rockets, launching satellites into earth’s orbit, often attain speeds up to 8 km/s. On the other hand, all units (given in options) are not suitable for expressing the speed of a rocket. Hence, your answer will be option [B].

We know that odometer is an instrument for measuring the distance travelled by a vehicle. Odometer records the distance travelled by a vehicle in kilometers.

Pendulum clocks are good to use among these options. To measure time intervals shorter than one day, a number of times measuring devices were invented in ancient times. Some of the important time measuring devices used in ancient times were: sundial, sand clock and water clock.

The option [B] is not relevant to unit of speed. Rest of all could be the unit of speed, where necessary. Hence, your answer will be option [B].

The unit of speed depends upon the unit of distance and the unit of time used. The standard unit of distance is meter and the standard unit of time is second. So, the standard unit of speed is meters per second. This unit of meters per second is written in short form as m/s.

If the distance time graph of an object is a straight line, it indicates that the object is moving with a uniform speed or constant speed i.e., its speed is not changing at all. The slope of a distance-time graph indicates the speed of the objects. If the distance time graph has a low slope then the object has low speed. On the other hand, if the distance time graph has a highest slope then the object has a higher speed.

The time measured by “Quartz clocks and watches” is much more accurate than that measured by clocks and watches which were available earlier. Thus, very accurate measurement of time is not possible by using “Quartz clocks and watches”. Quartz is a hard mineral consisting of silica. These days, the regular of oscillations or vibrations of a tiny quartz crystals when joined into an electric circuit, are used for measuring time very accurately.

The two extremely small units of time which are used for expressing very, very small-time intervals are “microsecond” and “nanosecond”. One microsecond is one-millionth of a second. A nanosecond is one-billionth of a second.

A bar graph is a diagram which shows information as bar or thin rectangles of different heights. In bar graph, the position and heights of the bars represent the values of the variable quantity about which information is given. This graph shows the object price increase with year, runs with over, selling market with respect to year. Bar graphs are frequently used in newspaper, magazines and TV to present various types of information in an interesting way. A bar graph is also known as a “histogram”.

We know that the fact that the time period of a given pendulum is constant was discovered by a scientist named “Galileo Galilei” just by chance. The periodic motion of a pendulum is utilized in pendulum clocks for measuring time. Remember, the pendulum clocks were big and bulky so they could not be carried everywhere is easily. In order to make small, light and portable clocks and watches a kind of modified pendulum was developed which is much smaller and compact than the traditional pendulum used in pendulum clocks, which is called balance wheel.

In order to solve this problem, we have to calculate the speed of both the trains separately. The train having higher speed will have travelled faster: We know that, Speed = Distance travelled / Time taken Distance travelled by train “A” = 150 km Time taken by train “A” = 3 h Speed of train “A” = 150 km / 3 h = 50 km/h Again, we know that: Speed = Distance travelled / Time taken Distance travelled by train “B” = 180 km Time taken by train “B” = 4 h Speed of train “B” = 180 km / 4 h = 45 km/h

The pendulum oscillates to-and-fro, the maximum displacement of the bob from its mean position on either side is called the amplitude of Pendulum. We know that the amplitude of oscillation of a pendulum is large or small the time taken for one complete oscillation a time period remains the same.

Explanation: The formula for the calculating speed is: Speed = Distance travelled / Time taken Here, Distance travelled = 70 m Time taken = 20 s So, putting these values in the above formula, we get: Speed = 70 m / 20 s = 3.5 m/s Thus, the speed of scooter is 3.5 meter per second.