very easy question.. come do it (1 Viewer)

[kooltrainer]

During a visit to the moon, an astronaut throws a rock vertically and it reaches a height of 20m. Acceleration due to gravity on moon is 1.6m/s/s. What is the speed at which it was thrown on the moon?

 

[RiSeAgAiNSt2538]

0.8eV = 1.28x10^-19J

E=hf

E=hc / wavenlength

wavelength = hc/E

= (6.6*10^-34 x 3*10^8) / 1.28*10^-19

= 1.5*10^-6 m

 

[xiao1985]

Huh?

Conservation of energy. At the max height, GPE is at max, KE = 0.
GPE at max = m x g x h = 32 m

When rock was thrown, GPE = 0 (relative to the starting point), KE = 1/2 mv^2

1/2 mv^2 = 32 m
v = sqrt (64) m/s = 8 m/s

If you really want to be vigorous, use change of GPE instead of GPE. But calculation would come down to be the same. (If my physics has not all rusted)

edit: oops

 

[Pwnage101]

uh isnt this a simple projectile Q???

everything is vertical, so no need to resolve into components

using : v^2 = u^2 +2as

0=u^2 +2*-1.6*20
64=u^2
u=8m/s up

 

[kooltrainer]

yeh i no.. but its a multiple choice question and there isnt 8m/s to choose from... must be error in question then..