Describe this journey in as much detail as possible.
Give values for velocities, acceleration and displacements.
Describe the motion of the car during the first 20 s.
The car has an initial velocity of 12 m/s.
From 0 to 20 seconds it moves at a constant velocity of 12 m/s.
What is the displacement of the car after 20 s?
In 20 s the displacement of the car is equal to the area of the rectangle.
Displacement = area of rectangle = 20 s × 12 m/s = 240 m.
Calculate the deceleration of the car from 20 s to 30 s.
At 30 seconds the car stops, its velocity is 0 m/s.
Acceleration of the car is the gradient of the graph =
acceleration = (0 m/s – 12 m/s) ÷ 10 s = -1.2 m/s2
The car has an acceleration of -1.2 m/s2 (or a retardation of 1.2 m/s2).
How far does the car move while decelerating?
The displacement while decelerating equals the area of triangle
displacement = 10 s x 12 m/s = 60 m
The car moves 60 m while decelerating.
What is the average velocity of the car during its entire journey?
The total displacement of the car = total area under the graph = 240 m + 60 m = 300 m.
The average velocity of the car over the whole journey =
average velocity = 300 m ÷ 30 s = 10 m/s.
The average velocity of the car is 10 m/s.