Class 7 Science Chapter 9 MCQ

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.

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].

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.

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

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].

Blinking of eyes is not a periodic phenomenon (i.e., it does not repeat after definite intervals of time), so we cannot measure the time using this phenomenon.

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

Remember, a pie chart is a kind of graph or diagram which shows the percentage composition of something in the form of slices of a circle which refers the whole circle as 100%. Pie chart can show the composition of air very easily.

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.

We should first convert the time of 15 minutes into hours by dividing it by 60 = 15 /60 hours = 0.25 hour i)In the 1st case: Distance travelled = Speed x time = 40 x 0.25 km = 10 km ii)In the 2nd case: Distance travelled = Speed x time = 60 x 0.25 km = 15 km Total distance: 10 km +15 km = 25 km

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.

In this problem, the speed is given in metre per second and the time is given in minutes. So, before putting in the formula for speed, we will have to convert time from minutes into seconds by multiplying the minutes by 60. Time taken = 15 minutes = 15 x 60 seconds = 900 s Speed = 2 m / s Distance travelled? (To be calculate) Now, Speed = Distance travelled / Time taken 2 = Distance travelled / 900 By cross multiple: Distance travelled = 2 x 900 m = 1800 m

The distance time graph for an object which stops moving is a straight line parallel to the time axis. When an object becomes stationary its speed is zero. So, a straight-line graph parallel to the time-axis shows that the speed of object is zero. Thus, a straight-line graph parallel to the time axis or a horizontal line graph tells us that the object has become stationary or it is not moving.

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.

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. Similarly, it will not be wise to express in years the time taken by you to cover the distance between your home and your school. Rockets, launching satellites into earth’s orbit, often attain speeds up to 8 km/s. On the other hand, a tortoise can move only with a speed of about 8 cm/s. Although snail is very slower animals comparing to tortoise, earthworm. The most appropriate unit for expressing the speed of a snail is mm/s.

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 distance time graph for an object which stops moving is a straight line parallel to the time axis. When an object becomes stationary its speed is zero. So, a straight-line graph parallel to the time-axis shows that the speed of object is zero.