simple projectile motion help plz! (1 Viewer)

[felixcthecat]

umm 2 questions for projectile motion i got off a book.. they used a wierd equation i havn't learnt and i wanna see if it could be done off the simple physics motion equations (u kno, those 3.. lolz)
the questions are..

1. a long jumper left the ground at an angle of 15 and jumped a distance of 7m. considering this result, calculate the velocity of the long jumper when leaving the ground

2. a volleyball player returns a volleyball, hitting the ball just above the gorund from a point int he middle of the baseline. the ball leaves the player's hand with a velocity of 12ms-1 at an angle of 50 to the horizontal, travelling directly towards opponents' baseline. The volleyball court is 18m long between the baselines, and the gymnasium ceiling is 5.5m above the floor
a) answer: max height reached = 4.3m
b) If the ball is not touched by any of the opponents, calcuylate whether the ball would land within the court.

^ don't understand 2)b)

they used a range equation as follows

R= (u(squared) x sin2B)/g

lol.. if u understand that typing.. but i havn't learnt that equation so i'm reluctant to use it.. there should be another way around but i just havn't touched the topic for too long.. help plz!!

 

[helper]

1.
y=u_yt+0.5a_yt²
0=u_yt+0.5*9.8t²
t=0 or u_y/4.9 Use second as that is landing

u_y=usin15
t=usin15/4.9

x=u_xt

u_x=ucos15

x=ucos15t
7=ucos15*usin15/4.9

7=u²cos15sin15/4.9


2.
(a)
v_y²=u_y²+2ay
0=u_y²-19.6y
y=(12cos15)²/19.6

(b) similar to 1 but calculate time of flight and then subst into x formula
If x is less than length of court it lands in

 

[felixcthecat]

ohh i get it now!! lol.. thanx

but i still don't think this is physics.. looks more like maths--

 

[insert-username]

Physics is based on Maths. You can't go very far in Physics without running into Maths.


I_F

 

[Riviet]

Those Newtonium formulae for objects in motion are derived using maths, I'm currently doing it in 4u maths at the moment in a topic called mechanics.

 

[rama_v]

ohh i get it now!! lol.. thanx

but i still don't think this is physics.. looks more like maths--

Real Physics is basically ALL maths, with physical concepts behind it. Its not, as the HSC sylabus writers think, based on Einstein and Plancks politcal views or how the manhattan project affects society

 

[felixcthecat]

.. just when i thought i could escape from maths in physics...... heh~ yea i remember deriving the 3 motions equation in maths a while back when doing motion..

 

[kobebryant8]

chanchan, phys exam is over, ready for prac. btw that question is in success one.lol

 

[felixcthecat]

umm... i'm guessing who u are... and yup it was out of successone~ they used an equation that we weren't taught!! but there wasn't much use of it i guess besides from shortening the writing out to 3 lines

 

[helper]

Real Physics is basically ALL maths, with physical concepts behind it. Its not, as the HSC sylabus writers think, based on Einstein and Plancks politcal views or how the manhattan project affects society

I'd say it is the other way round. Physicists identify a physical concept and then try to develop a mathematical model to explain and/or describe the principle. Same effect really.

Learns the maths and you think you understand physics but really you have to understand and interpret the maths to understand the physics.

 

[rama_v]

I'd say it is the other way round. Physicists identify a physical concept and then try to develop a mathematical model to explain and/or describe the principle. Same effect really.

Learns the maths and you think you understand physics but really you have to understand and interpret the maths to understand the physics.

Perhaps, but either way there's no escaping that you can't do real quantitative physics without being adept at maths. Which is something the HSC sylabus doesn't seem to remember.

 

[helper]

Perhaps, but either way there's no escaping that you can't do real quantitative physics without being adept at maths. Which is something the HSC sylabus doesn't seem to remember.

No arguments there, too much history, philosophy and sociology in the new syllabus. Trouble is most 11 and 12 students don't have the maths ability to understand 20th Century Physics and they wanted to introduce it somehow.

Black body radiation is a perfect example. The syllabus mentions it but to describe Planck's idea you need to understand probability and distributions. So people say they don't understand because the maths behind it are not explained.