i. The metallic ball is called the bob of the pendulum.
ii. The symbols of all units are written in singular.
iii. The time taken by the pendulum to complete one oscillation is called its time period.
iv. One microsecond is one millionth of a second.
v. A nanosecond is one billionth of a second.
vi. The distance-time graph for the motion of an object moving with a constant speed is a straight line.
i. The basic unit of time is second. True
ii. Every object moves with a constant speed. False
iii. Distances between two cities are measured in kilometres. True
iv. The time period of a given pendulum is not constant. False
v. The speed of a train is expressed in m/h. False
vi. Clocks that measure such small time intervals are used for scientific research. True
Ans. The basic unit of time is a second. Its symbol is s.
Ans. Basic unit of speed is metre per second (m/s).
Ans. Speedometer is an instrument that indicates the speed of a vehicle.
Ans. Distance-time graph represents the speed of an object.
Ans. The distance moved by an object in a unit time is called its speed.
Ans. The to and fro motion of an object is called oscillatory motion.
Ans. Motion is a change in position of an object over time.
Ans. Circular motion is rotation of an object along a circular path.
Ans. The to and fro motion of a simple pendulum is an example of a periodic or an oscillatory motion.
Ans. If the speed of an object moving along a straight line keeps changing, its motion is said to be non-uniform.
Ans. An object moving along a straight line with a constant speed is said to be in uniform motion.
Ans. The smallest time interval that can be measured with commonly available clocks and watches is one second.
Ans. A simple pendulum consists of a small metallic ball or a piece of stone suspended from a rigid stand by a thread. The metallic ball is called the bob of the pendulum.
Ans. Many time measuring devices were used in different parts of the world before the pendulum clocks became popular. Sundials, water clocks and sand clocks are some examples of such devices.
Ans. Nowadays most clocks or watches have an electric circuit with one or more cells. These clocks are called quartz clocks. The time measured by quartz clocks is much more accurate than that by the clocks available earlier.
Ans. Speed or average speed is the total distance covered divided by the total time taken. Thus,
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