Two photographic pictures depict a boy throwing a rock, taken at interval 2 seconds between them?

Question

On the second picture the rock appears 10m higher than on the first one. At what moment did the rock reached the maximum height, and what was that height?

Answer 1

Let's deal with the vertical motion only, neglecting air resistance.
a = -g = -9.81 m/s^2

at t = 0, y = 0
at t = 2, y = 10

y = ut - 1/2 gt^2
10 = 2*u - 2g
u = 5+g m/s

Max height occurs when
dy/dt = 0 = u - gt
is t = u/g = 1.51 seconds

Max height = u^2 / (2g) = 11.18 m above the position depicted by the first picture.

Interesting, the rock was actually on its way down in the second photo.

Answer 2

Actually, thinking about it, just use the equations of motion!

You have three parameters:

s [displacement] = +10 meters
u [inital velocity] is unknown
v [final velocity] is unknown
a [acceleration] = -10 m/s²
t [time] = +2 seconds

[+ve is up, -ve is down]

Plugging that into s=ut+½at² gives u = +5 m/s.

This implies that the rock is at the maximum height in ½ a second (v=u+at; where v = 0, u and a are the same gives t = ½ second).

Using v²=u²+2as gives 1.2 metres.

Don't give up, problems are generally solvable, remember or look up your SUVAT equations, remember you only need any three parameters for these problems.

[I think I've got my maths wrong somewhere. But the principle is sound.]

Answer 3

Rock-throwing is the equivalent of bricks thrown at officers for the period of the riots in la. that's misguided and imperils officers doing their accountability. it's time to militarize our border till a secure hi-tech fence might properly be geared up. a solid, properly-lit fence, with action sensors and cameras, heavily patrolled with armed BP. BP outposts must be typical each 50 miles or so, manned and able to speedy reaction to incursion tries. The southern border desires to be secured first, then the northern one.

Answer 4

Not enough information.
Can't be solved without relating the times
of the pictures to the release of the rock.

Answer 5

Definitely not enough information. How can you figure out what the maximum height is if you don't know initial velocity?

Answer 6

There are other variables that would come into account to figure it out. You could estimate, I guess, but it still wouldn't be exactly right.

Answer 7

not enough info

Answer 8

exactly what i had in mind