Table of contents | |
Defining Acceleration | |
Speeding Up and Slowing Down | |
Solved Example | |
Estimating Accelerations |
The equation for acceleration can be rearranged with the help of a formula triangle as shown:
Example: A Japanese bullet train decelerates at a constant rate in a straight line.The velocity of the train decreases from 50 m/s to 42 m/s in 30 seconds.
(a) Calculate the change in velocity of the train.
(b) Calculate the deceleration of the train, and explain how your answer shows the train is slowing down.
Part (a)
Step 1: List the known quantities
Initial velocity = 50 m/s
Final velocity = 42 m/sStep 2: Write the relevant equation
change in velocity = final velocity − initial velocityStep 3: Substitute values for final and initial velocity
change in velocity = 42 − 50 = −8 m/sPart (b)
Step 1: List the known quantities
Change in velocity, Δv = − 8 m/s
Time taken, t = 30 sStep 2: Write the relevant equation
Step 3: Substitute the values for change in velocity and time
a = −8 ÷ 30 = −0.27 m/s
Step 4: Interpret the value for deceleration
The answer is negative, which indicates the train is slowing downExam Tips: Remember the units for acceleration are metres per second squared, m/s2
In other words, acceleration measures how much the velocity (in m/s) changes every second, m/s/s.
Exam Tip: You should be able to estimate the magnitude of everyday accelerations. Memorise the examples given in the table to develop a sense of the magnitude of different accelerating objects.
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