ELECTRIC TRACTION – PART – 06 - IMPORTANT TERMS IN TRACTION AND TWO PROBLEMS

DIFFERENCE BETWEEN DISTANCE AND DISPLACEMENT

DISTANCE is a scalar quantity that refers to "how much ground an object has covered" during its motion.

DISPLACEMENT is a vector quantity that refers to "how far out of place an object is"; it is the object's overall change in position.

DIFFERENCE BETWEEN SPEED AND VELOCITY

SPEED – The rate of change in distance with respect to time.   Since speed is built from distance, a scalar quantity, then speed is also a scalar quantity.  This means it carries no direction information with it.

VELOCITY – The rate of change in displacement with respect to time.  Since displacement is a vector quantity, then velocity is also a vector quantity.  It has both magnitude and direction.

Both speed and velocity are typically measured in units of miles per hour, kilometers per hour (Km/hr), or meters per second (m/s).

INSTANTANEOUS SPEED

The speed at any given instant in time.

CREST SPEED OR PEAK SPEED

This is the maximum speed of the train during a run.

AVERAGE SPEED

This is the average speed of a train during a run. It is equal to the total distance divided by the total time.

Average speed = total distance covered / total time taken

SCHEDULE SPEED

This is the ratio of the distance between two destinations and the total time to cover the distance, including time wasted in stoppages.

Schedule speed = Distance / [time for run + time for stop]

FACTORS AFFECTING SCHEDULES SPEED

(a) Peak speed                 (c) Braking retardation

(b) Acceleration               (d) Duration of stoppages.

PROBLME - 01

A train has a speed of 60 km/hr. between two stops, 5 km apart. The duration of stop is one minute. The acceleration and retardation are 2 km/hr./sec. and 3 km/hr./sec. respectively. Calculate the maximum speed of the train.

PROBLME - 02

A train is required to run between two stations 1.5 km apart at the average speed of 40 km/hr. The run is to be made to a simplified quadrilateral speed-time curve. If the maximum speed is to be limited to 60 km/hr. acceleration to 2 km/hr. /sec. and coasting and braking retardation of 0.16 km/hr./sec. and 3.2 km/hr./sec. respectively. Calculate the duration of acceleration, coasting and braking periods.