Answer:
The speed of the rock when it is at height h/4 is
.
Explanation:
At maximum height the final velocity of the rock is equal to 0. Let u is the initial velocity of the rock. Using the conservation of energy to find it as :
.......(1)
We need to find the speed of the rock when it is at height h/4. Let v' is the speed. Using 3rd equation of motion as :

here a = -g and s = h/4

Using equation (1) :

So, the speed of the rock when it is at height h/4 is
. Hence, this is the required solution.
Answer:
New force, 
Explanation:
The electrostatic force between two spheres is given by :

According to given condition, each of the spheres has lost half its initial charge, new force is given by :



So, the new force becomes (1/4)th of the initial force. Hence, the correct option is (d).
This is reactivity. It describes how easily one substance reacts with another
Answer:
Find two boxes just a bit smaller than the other. The long sides of the box should be less than twice as long as the short side of the boxes. The smaller box should fit inside the larger box with about 1 inch in each direction to spare. The boxes can be cut down so that they fit together properly. Leave the flaps on the boxes. Buy a small sheet of Plexiglas (tm) a little bit smaller than the width and length of the top of the box. You will also need four pieces of cardboard to use for reflectors.
Explanation:
Chemical Name: Sodium Hydroxide