October 19, 2019, 07:13:46 am

### AuthorTopic: A few easy physics questions that I would like help with-plz  (Read 1158 times) Tweet Share

0 Members and 1 Guest are viewing this topic.

#### fELiX

• Victorian
• Posts: 6
• Respect: 0
##### A few easy physics questions that I would like help with-plz
« on: November 14, 2007, 01:10:59 pm »
0
1) A ball is thrown vertically upwards and returns to the throwers hand. During its flight, the speed of the ball is: constant/increasing/decreasing/increasing and decreasing (circle one)

2) An archer fires an arrow vertically into the air from groung level at a speed of 12m/s.
a)Find initial vertical acceleration of arrow
b)For how long will the arrow be in the air
c)What is the acceleration of the arrow at the top of its flight
d)What maximum height does the arrow reach
e)What is the speed of the arrow just before it impacts with the ground
f)Describe any forces acting on the arrow during its flight and any variations in these forces.

Thank You

Cheers

#### cara.mel

• Guest
##### A few easy physics questions that I would like help with-plz
« Reply #1 on: November 14, 2007, 02:09:27 pm »
0
1. It's decreasing when it travels up, increasing when it goes down

2. a) We live in a world without air resistance, so acceleration is always -9.8m/s^2 or -10. Generally, in physics we say it's -10 because it's an easier number, but go with whatever your teacher tells you to use.
b) There is more than one way to do this question. I am going to find the time it takes to reach the top of its 'flight', and then double it (seeing as it takes the same time to go up and come down)
So a=-10, u=12, v=0, t=?
v=u+at
0=12 - 10t
10t = 12
t=1.2s to reach top => total flight = 2.4s
c) acceleration is constant -> -10m/s^2
d) a=-10, u=12, v=0 (because top of flight), y=? (you can use your 't' value from before, but it is a good idea not to in case you made a mistake)
v^2 = u^2-2ay
144 = 20y
y = 144/20 m = 7.2 I think
e) Flight is symmetrical (from ground level to ground level) -> hits at same speed it leaves at -> 12m/s
f)This depends if the question is with or without air resistance (you never do calculations with air resistance because it is too hard)
Without air resistance, the only force is acceleration downwards, which is constant.
With air resistance, there is also a force in the opposite direction to the direction it's traveling in, which is larger when it is going faster (so at the top there is no air resistance force)

#### kido_1

• Victorian
• Posts: 526
• Respect: +6
##### Re: A few easy physics questions that I would like help with
« Reply #2 on: November 14, 2007, 03:48:37 pm »
0
Quote from: "fELiX"
1) A ball is thrown vertically upwards and returns to the throwers hand. During its flight, the speed of the ball is: constant/increasing/decreasing/increasing and decreasing (circle one)

2) An archer fires an arrow vertically into the air from groung level at a speed of 12m/s.
a)Find initial vertical acceleration of arrow
b)For how long will the arrow be in the air
c)What is the acceleration of the arrow at the top of its flight
d)What maximum height does the arrow reach
e)What is the speed of the arrow just before it impacts with the ground
f)Describe any forces acting on the arrow during its flight and any variations in these forces.

Thank You

Cheers

What is meant by initial vertical acceleration?
I think it might be either -10m/s/s or maybe 0(Just taking a punt)
oping for an ENTER of 99+

#### Galelleo

• Victorian
• Forum Obsessive
• Posts: 405
• Respect: 0
##### A few easy physics questions that I would like help with-plz
« Reply #3 on: November 14, 2007, 04:21:33 pm »
0
vertical accelleration is always gravity. in physics we take it as -10m/s^2... in maths you use 9.8
Light a man a fire and he will be warm for the rest of the night.
Light a man ON fire and he will be warm for the rest of his life.

#### karina

• Victorian
• Trailblazer
• Posts: 31
• Respect: 0
##### A few easy physics questions that I would like help with-plz
« Reply #4 on: November 25, 2007, 02:07:04 pm »
0
i ignored general maths advanced this yr especially the kinematics section because i did 3/4 phsyics, but i took 10 as acceleration all the way trhough the exam! it was annoying, why must maths complicate everything !
methods, physics (2007)
english, further, chem, specialist, physics (2008)

#### Timtasticle

• Victorian
• Trendsetter
• Posts: 104
• Respect: 0
##### A few easy physics questions that I would like help with-plz
« Reply #5 on: November 26, 2007, 10:42:59 am »
0
Quote from: "karina"
i ignored general maths advanced this yr especially the kinematics section because i did 3/4 phsyics, but i took 10 as acceleration all the way trhough the exam! it was annoying, why must maths complicate everything !

I think it's more a matter of VCE Physics simplifying everything.