Form 4 Physics | Chapter 2 | Note

Hmmm... seems like most of the students still confused with the trigonometry although they reached Form 5. So, I am going to give you a tips on how to solve question about it now.

Usually, we need to know about sin and cos only for SPM level.

Figure 1

Figure 2

Tips: Always use cos for the axis which sticks to the angle given and use sin for the axis which does not stick to the angle given.
Now, you don't need to worry which trigonometry should you use since it's as easy as this. Still not confident yet? Let's try a question.

Example:

Figure 3

The picture above shows that a girl is trying to stop her dog which is running forward with a force of 40N. How much force should the girl use to pull her dog to make her dog stop moving?

Solution:
*Draw a free-body diagram first!

Figure 4

The girl needs to pull 40N to the right since her dog is running to the left with force of 40N.

Figure 5

But!!! We're not going to look for the force to the right, but 30° above the horizontal axis.
Remember the note above? We're going to use it now.

Figure 6

The force to the right in figure 5 is 40N.
The force to the right in figure 6 is F cos 30°.
Both of them are equal, so:
40 = F cos 30°
F = 40 / cos 30°
F = 40 / 0.866
F = 46.19N

∴ The girl apply foce of 46.19N at 30° above horizontal axis to pull the dog to come to a stop.

Easy, right?
Ask if you have any question!
Wish you all the best!