Answer:
4.5 m/s
Explanation:
The rock must barely clear the shelf below, this means that the horizontal distance covered must be
while the vertical distance covered must be
The rock is thrown horizontally with velocity 
, so we can rewrite the horizontal distance as
where t is the time of flight. Re-arranging the equation,
(1)
The vertical distance covered instead is
where we omit the term 
since the initial vertical velocity is zero. From this equation,
(2)
Equating (1) and (2), we can solve the equation to find :
The strength, and possibly the shape and direction, of the electric field
around a charged particle depends on the location of the particle.
If the process of measuring the field causes the particle to move, then
the measurement you get wouldn't mean anything.
Your measurements wouldn't show the ACTUAL field around the particle.
They would show what the field is like AFTER something comes along
and distorts it, and that's not what you're trying to measure.
It would be like carrying a flame thrower into a freezer when you go in
to measure the temperature in there.
Or if you had to measure how much light is leaking into a dark room,
and you carried a flashlight with you to see your way around in there.
For the third one on the top you can put to get solar panels on your roof
4. 1 and 2 only.
1. the downward force is the force of gravity.
<span>2. The upward force exerted is the Normal reaction from the floor.</span>
