Equations of Motion

We can use the Equations of Motion to calculate the speed of an object under different circumstances.  These are quantities are involved in linear motion, movement in a straight line:

Quantity

Physics Code

Units

Distance

s

m

Speed at the start

u

m/s

Speed at the end

v

m/s

Acceleration

a

m/s2

Time

t

s

1.  Speed at finish = speed at start + change in speed

change in speed = acceleration × time.

Speed at end = speed at start + (acceleration × time)

2.

3.  Distance = average speed × time

 

4. 

 

Question 4

A car is travelling at 30 m/s and takes 10 seconds to acceleration to a new speed of 35 m/s.  What is its acceleration? 

ANSWER

Question 5

A brick falls off the top of a wall under construction and drops into a bed of sand 14.5 m below.  It makes a dent in the sand 185 mm deep.  What is:

a)       The speed of the brick just before it hits the sand.                                                         

b)       Its deceleration in the sand.                                                                                          

c)       What would happen to a person undergoing that deceleration? 

ANSWER

                    

In many examples we can ignore air resistance, although you will know for yourselves that the faster you go on a mountain bike, the harder you have to pedal.  This is because of the effects of friction and air resistance (drag).  We will look at this next in Terminal Velocity.                  

Presentation Equations of Motion
Terminal Velocity BACK to Start of Topic 1 BACK to Topic 3
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