**(New tips are continually
added to these pages. Check back in a few months' time for more)**

**TOPIC 2:
Kinematics and Dynamics**

__Tip 1:__

The 4 main equations in Kinematics are:

*v = u + at
s = ut + ½at ^{2}
v^{2} = u^{2} + 2as
s = *[(

These equations should not be used
in their raw form, as written above. Instead, you should break them into
*x* and *y*
components, as follows:

*
v _{x} = u_{x} + a_{x}t
v_{y} = u_{y}
+ a_{y}t*[(

s_{x} = u_{x}t + ½a_{x}t^{2 } s_{y} = u_{y}t + ½a_{y}t^{2}

v_{x}^{2} = u_{x}^{2} + 2a_{x}s_{x } v_{y}^{2} = u_{y}^{2} + 2a_{y}s_{y}

s_{x} =

For example, in a projectile
problem, where a canon ball is projected at a speed of 20 m s^{-1} at an angle of 30º to the
horizontal, it would be wrong to just let *u* = 20 m s^{-1} and start calculating. Instead,
you should use *u*_{x} = 20 cos 30º = 17 m s^{-1} and *u*_{y} = 20 sin 30º = 10
m s^{-1}.

__Tip 2:__

Instead of just writing *F* =
*ma*, it
is better to write it as å*F* = *ma*, since it is the resultant
force that is equal to mass x acceleration.

The left hand side of the equation
contains the resultant of all forces acting on the body. Note that the weight of the
body, *mg*, should be part of these forces (ie. on the left hand side of the equation), and
not on the right hand side (a common mistake by students is to replace "*ma*" with
"*mg*").

__Tip 3:__

When solving Dynamics problems, always:

1. Draw the free-body-diagram, with all forces acting on the body.

2. Indicate which direction to assign as the positive convention.

3. Indicate the
direction of acceleration and label it "*a*".

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