Define variable speed. Support your answer by two examples.

(i) A car parked on roadside.

(ii) A truck moving with constant speed.

$\left(\mathrm{a}\right)$ Graph shows a non-uniform speed?
$\left(\mathrm{b}\right)$ Graph shows the speed is zero?
$\left(\mathrm{c}\right)$ Graph shows uniform speed?

The gap between two events is called time. In earliest days solar day was taken as unit of time. Later one man switched on devices such as sundials and sand clock. Now these days different types of clocks such as wall clock, wrist watch, stopwatch, digital watch etc., are available to measure time period. Mahesh wanted to know its basic principle and significance, so he contacted his friend Sudhir. Sudhir explained its details and significance properly.

Answer the following question based on above information:

What are the values displayed by Sudhir?

The gap between two events is called time. In the earliest days, the solar day was taken as the unit of time. Later one man switched on devices such as sundials and sand clocks. Now these days different types of clocks such as wall clocks, wristwatches, stopwatches, digital watches, etc., are available to measure the time period. Mahesh wanted to know its basic principle and significance, so he contacted his friend Sudhir. Sudhir explained its details and significance properly. 
Answer the following question based on the above information: How does sundial work? Can it show the time during the night?