VCE Physics Question Thread!

[KiNSKi01]

Hi, I'm struggling with two physics questions, hoping for a little bit of help please!
Thanks in advance!

Check my response in other thread 

[KiNSKi01]

Need some help with a fairly basic tethered objects question and I'm getting a different answer to the one provided.

A block weighing 2kg is accelerated by a falling weight (0.5kg). Calculate the tension in the cord if 2kg block experiences a fricitional force of 1.5N as it slides on the table.

First I considered the whole body assuming it experiences uniform acceleration. The only two forces acting on the whole body are the frictioon force and gravity. Therefore I calculated the resultant force to be 0.5 x 9.8 subtract 1.5. Meaning the system was accelerating at 1.36 m/s^2.

Then I looked at the forces acting on the 2kg block (drag and tension). and then Fresultant= 2 x 1.36 and calculated the tension to be 4.22 N.
The answer is 4.3N (yeah i know HUGE difference) but this answer couldn't be due to rounding 

EDIT they used g as 10 instead of 9.8    -_____- 

[Yertle the Turtle]

EDIT they used g as 10 instead of 9.8    -_____- 

I HATE it when they do that. Checkpoints do that and it is the most annoying thing ever!

[sweetiepi]

EDIT they used g as 10 instead of 9.8    -_____- 

I HATE it when they do that. Checkpoints do that and it is the most annoying thing ever!

Some of the older checkpoints questions could be from the old study design, where g was 10, instead of 9.8. Also note that is obviously the case in past VCAA exams before last year's one.
Otherwise,your working is right KiNSKi for using 9.8 instead of 10.
(Sorry that I didn't see this before aha)

[Guideme]

In a tennis match at Kooyong a girl receives a serve which is traveling at 30m/s south just prior to hitting her racket. Immediately after leaving her racquet it is travelling at 25m/s north. Specify fully the change in velocity she gave the ball
I think the answer is 55m/s but it seems too simple to be true haha.

Help pls
Thx in advance

[Yertle the Turtle]

In a tennis match at Kooyong a girl receives a serve which is traveling at 30m/s south just prior to hitting her racket. Immediately after leaving her racquet it is travelling at 25m/s north. Specify fully the change in velocity she gave the ball
I think the answer is 55m/s but it seems too simple to be true haha.

Help pls
Thx in advance

You use the formula v=v2-v1 and specify either North or South as being positive. Then you simply do v=25-(-30), so v=55m/s North, since a velocity requires a direction as well as a magnitude. Hope this helps.

[Vaike]

In a tennis match at Kooyong a girl receives a serve which is traveling at 30m/s south just prior to hitting her racket. Immediately after leaving her racquet it is travelling at 25m/s north. Specify fully the change in velocity she gave the ball
I think the answer is 55m/s but it seems too simple to be true haha.

Help pls
Thx in advance

Marvin's on the money. However I thought I'd still post this, as kind of a guide on how to best set out your working, It's pretty easy to mess this stuff up in a rush, so I found it really helpful to always clearly set out my working like this to avoid any potential errors.

Spoiler

Remember, velocity is a vector, this means it requires both direction and magnitude! Drawing a diagram usually helps with this, just make sure to draw the arrows the correct relative sizes!

[skrt skrt]

Good resources for learning special relativity?

[Calebark]

Good resources for learning special relativity?

I didn't do the new study design, so I only know of the YouTube Channel ran up the new Edrolo physics guy, which is located here.

[sweetiepi]

I didn't do the new study design, so I only know of the YouTube Channel ran up the new Edrolo physics guy, which is located here.

That guy is 100% a baller. Definitely rate this one too

[skrt skrt]

Why is that if two projectiles are  launched from the same height have the same time to fall to the ground?
Initial horizontal velocity from both objects is 5m/s and 2m/s, and the height is 1.8m

[Yertle the Turtle]

Why is that if two projectiles are  launched from the same height have the same time to fall to the ground?
Initial horizontal velocity from both objects is 5m/s and 2m/s, and the height is 1.8m

This is because the acceleration due to gravity is the same for all objects is 9.8m s^-2 and if you are disregarding air resistance they will all fall at the same time.

[Shadowxo]

Why is that if two projectiles are  launched from the same height have the same time to fall to the ground?
Initial horizontal velocity from both objects is 5m/s and 2m/s, and the height is 1.8m

I'd also just like to add that you can split the acceleration and speed etc into horizontal and vertical directions. Vertically, they both start off at the same height (1.8m), and the same vertical velocity (0 m/s) and having the same downwards acceleration from gravity (9.8 m/s^2) - gravity only acts vertically.
Therefore their horizontal displacement / velocity / acceleration is irrelevant when calculating when they'll hit the ground (but it will determine how far the ball travels)

[hemalw0914]

Need help with some homework - Thermodynamics U1

1)Give two reasons why you feel cooler when the wind is blowing than you would in still air at the same temperature.

2) In humid weather, evaporation of perspiration takes place as it does in dry weather. However, the cooling effect is greatly reduced. Why?

3) In hot weather, sweat evaporates from the skin. Where does the energy required to evaporate the sweat come from?

[skrt skrt]

Thanks for the responses but why doesnt mass affect this, like mg?