Draw velocity-time graphs for the following situations:
$(i)$ When a body is moving with uniform velocity.
$(ii)$ When a body is moving with variable velocity,but uniform acceleration.
$(iii)$ When a body is moving with variable velocity,but uniform retardation.
$(iv)$ When a body is moving with variable velocity and variable acceleration.

(N/A) The velocity-time graphs for the given situations are as follows:
$(i)$ For uniform velocity: The graph is a straight line parallel to the time axis,indicating that velocity does not change with time.
$(ii)$ For variable velocity with uniform acceleration: The graph is a straight line inclined to the time axis with a positive slope,indicating a constant rate of increase in velocity.
$(iii)$ For variable velocity with uniform retardation: The graph is a straight line inclined to the time axis with a negative slope,indicating a constant rate of decrease in velocity.
$(iv)$ For variable velocity and variable acceleration: The graph is a curve,indicating that the rate of change of velocity (acceleration) is not constant.