Answer:
Time taken, 
Explanation:
It is given that, a small metal ball is suspended from the ceiling by a thread of negligible mass. The ball is then set in motion in a horizontal circle so that the thread’s trajectory describes a cone as shown in attached figure.
From the figure,
The sum of forces in y direction is :


Sum of forces in x direction,

.............(1)
Also, 
Equation (1) becomes :

...............(2)
Let t is the time taken for the ball to rotate once around the axis. It is given by :

Put the value of T from equation (2) to the above expression:


On solving above equation :

Hence, this is the required solution.
Work Done = Force x Distance Moved
Work Done = 25 x 15 = 375 Joules
Answer: 
Explanation:
This problem can be solved by the following equation:

Where:
is the change in kinetic energy
is the electric potential difference
is the electric charge
Finding
:


Finally:

Formulae for Kinetic energy is:
Kinetic Energy= 1/2xmassx(velocity)^2
For comparison we need to have same units,thus we convert 10g into Kg.
10g/1000=0.01Kg
Input the value of bullet in the formulae;
Kinetic Energy= 1/2x0.01kgx(400)^2
K.E=800J
Input value of the ball:
Kinetic Energy=1/2x80kgx(6.5)^2
K.E=1690J
Which means that th Energy of the ball is more than the bullet.