May 25, 2019, 03:16:48 am

### AuthorTopic: Projectile Motion  (Read 93 times) Tweet Share

0 Members and 1 Guest are viewing this topic.

#### christopher.farag

• Fresh Poster
• Posts: 2
• Respect: 0
##### Projectile Motion
« on: April 22, 2019, 10:24:59 pm »
0
Hey,

I was teaching myself projectile and have gotten a bit confused. When is it that the angle found needs to be left negative, or the positive value needs to be taken?

Eg in question 4d attached, the angle of -8 degrees must be absolute valued, to be +8.

However in question 2cii attached, the negative value is kept as negative.

Slightly confused.

#### RuiAce

• HSC Lecturer
• Honorary Moderator
• Great Wonder of ATAR Notes
• Posts: 8328
• "All models are wrong, but some are useful."
• Respect: +2231
##### Re: Projectile Motion
« Reply #1 on: April 22, 2019, 10:48:49 pm »
+4
Technically speaking, that $-8^\circ$ is supposed to be kept negative. The negative is a consequence of how the projectile lands during its downwards journey, and hence its inclination at landing should be somewhere below the horizontal, and not above.

Perhaps, in the Cambridge textbook, what the authors were thinking is that if we just say angle, we mean its magnitude only (especially since the angle is obviously negative in such a scenario). Whereas when they say "angle of inclination", an inclination angle can only be positive when the inclination reflects something above the horizontal, and hence should be treated as a signed quantity.

In the HSC, either such discrepancy would not exist, or they have to accept any conclusion provided the working out is correct.