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.

The movement of an objects is called motion, not be “stationary-motion”.

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

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

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

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].

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].

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].

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.

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].

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 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 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.

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 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”.

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.

We know that the distance time graph is also called “Line graphs”. This line graph shows the variation of distance travelled by a moving object with time. A line graph can also be drawn to show the variation of any other related quantities such as a variation of weight of a man with age. So, here option [C] is the correct answer.

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.

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.