PHSI191

This is an overview of PHSI191 notes. In the complete version examplery questions will be provided to emphasise on the concepts and the equations that are supposed to be used.

Often a quicker way of calculating acceleration, velocity or displacement is to use some equations that are worked out from the D-T and V-T graphs. The symbols for displacement, initial velocity, etc. are shown on the diagram.

You can now use the equations that are listed below to calculate the velocities, displacements and accelerations.

s = vt Only use this if a = 0

v = u +at
v² = u² + 2as
s = ut + ½ at²

u may be indicated as v(i) ie. initial velocity and s may be denoted as d ie. displacement

What if velocity and acceleration are in different directions?

To show different directions use a positive or negative sign. It doesn’t matter whether you choose up or down, left or right as positive, as long as you stick to it for the rest of the question.

e.g. if you are going to the right at 10ms^-1 but accelerating to the left (i.e. decelerating) at 2ms^-2 then u = +10ms^-1 and a = -2ms-

Acceleration due to Gravity (Ignoring Friction)

Objects in a gravitational field experience a downwards force – their weight. If unbalanced, this will produce an acceleration downwards. This crops up frequently in A-level questions. However, it’s easy to deal with. Simply always use acceleration, a = g = 9.81 ms^-2 downwards.

For example, drop a stone from a cliff.
Initially, t = 0, u = 0, and a = + 9.81 ms^-2 (Note – I’ve chosen down to be positive here)
OR
throw a stone upwards at 10 ms^-1

Initially, t = 0, u = 10ms^-1 and a = g = -9.81ms^-2. (Note – I’ve chosen up to be positive here, just to be difficult – but also to show that it doesn’t matter which one you choose as long as you stick to it.)

From here, you can go on and use equations of motion to solve.

For health science first year treat g as 10 m per second squared.
Tips for exams:
In the real blogspot dedicated for phsi191 I will be posting final exam questions related to the concept and I will give step to step instructions on how to answer all these examplery questions.