easy Physic. that i need help with (1 Viewer)

[chazza]

During a visit to the moon an astronaut throws a rock vertically and its reaches a height of 20.0m. Acceleration due to gravity on moon is 1.6ms^-2 what is the speed at which it was thrown?

a) 25.3m/s b) 62.6m/s c) 640m/s d) 3920m/s

ALSO

what is the De Broglie wavelegth of an electron whose speed is half of the speed of light?

a) 3.6 x 10^-12m
b) 4.4 x 10^-11m
c) 4.9 x 10^-12m
d) 1.2 x 10^-11m

can any1 help me..
and can you show working out.. please.. thanks

 

[Tommy_Lamp]

v^2y = u^2y +2as

vy = 0, uy = ?, a = 1.6^-2, s = 20

work it from there

dont have my calc but i think its a

 

[wogboy]

During a visit to the moon an astronaut throws a rock vertically and its reaches a height of 20.0m. Acceleration due to gravity on moon is 1.6ms^-2 what is the speed at which it was thrown?

Projectile motion, use v^2 = u^2 + 2as to solve
u^2 = v^2 - 2as
v = 0, a = -1.6 m/s^2, s = 20.0 m
-> u^2 = 64
-> u = 8 m/s

Looks like none of those answers are correct ...

what is the De Broglie wavelegth of an electron whose speed is half of the speed of light?

The formula is L = h/(mv), where L is the De Broglie wavelength, m = mass, v = speed.

L = 6.6 * 10^-34 / (9.1 * 10^-31 * 0.5 * 3 * 10^8) = 4.8 * 10^-12 m, so I guess c) is the closest answer.

Side Note: Technically L = h/mv isn't correct for really high speeds such as in this question, due to relativistic effects. The more correct relativistic formula is L = h/(mv) * sqrt(1 - (v/c)^2) where m is the rest mass (of course you can use L = h/mv if you account for mass dilation), making the real answer 4.2 * 10^-12 m. You don't need to worry about this though, just use the classical (non relativistic) formulas when answering these sorts of questions.

 

[Rorix]

q1 seems like a typo, 200m gives you a

 

[Tommy_Lamp]

hang on, the acceleration due to gravity on the moon is 1.6, not 1.6^2 (i think), so maybe if u use that value itll come out correct

 

[chazza]

Thanks wogboy for your help and answers, i also got 8m/s for the 1st question, I thought I was wrong, now i guess the papers is wrong... heheh

q1 seems like a typo, 200m gives you a

heheh seems like there is a typo in the papers

hang on, the acceleration due to gravity on the moon is 1.6, not 1.6^2 (i think), so maybe if u use that value itll come out correct

naa man..the solution given are wrong.. i think there is somthing wrong with the paper...

BTW.. thanks to ALL you guys for helping me out

 

[Tommy_Lamp]

ah m'k, nprbs

 

[lotta cooties]

what is this de broglie thing? i have never seen it before in my life.

 

[angelicdevil]

im wit lotta cooties, i have never seen than before and its got me majorly confuzzled

 

[gordo]

its part of the quanta to quarks elective

lambda = h / mv

 

[gordo]

so for your answers

the wavelength will be

h (planks constant) divided by (mass of e) . 1/2 c
= 6.625 x 10^-34 / (9.109 x 10^-31 x 1.5 x 10^ 8)
= 4.85 x 10^-12 m
or c

 

[angelicdevil]

oh yea! kool thanx.. i just never heard of that formula but now i do remember using it

 

[Jase]

Jeez how can someone throw a rock at over 30m/s, thats over 100km/h, and yet only reach 20m.. and with the g on the moon, it would reach even higher.
In fact, the escape velocity of the moon is 8000km/h. That last answer means this astronaut would have the arm power to launch a damn rocket!

lol. Well those solutions are gay.. what paper is this?

 

[mojako]

its Ruse 2002 trial
http://www.boredofstudies.org/mirror/2004/James Ruse Physics Trials/JR_Physics_Trial_2002.pdf

Ruse exam has a typo???

BTW can someone give the answers to the MCs? There are quite a few Im not sure of.

To get everyone started, my answers:
2. C
3. C
4. D
5. C
6. B
7. C
8. C
9. B
10. D
11. B
12. A
13. A
14. C
15. D