**Answer:**

**Explanation:**

The energy lost due to air friction is equal to the mechanical energy lost by the parachutist during the fall.

The initial mechanical energy of the parachutist (at the top) is equal to his gravitational potential energy:

where

m = 20.1 kg is his mass

is the acceleration due to gravity

h = 662 m is the initial heigth

The final mechanical energy (at the bottom) is equal to his kinetic energy:

where

v = 7.12 m/s is the final speed of the parachutist

Therefore, the energy lost due to air friction is:

**Answer:**

**Explanation:**

Let be the time required to make one revolution.

Let be the radius of the circular path.

Let be the distance travelled by ball in one revolution.

**As we know,the distance travelled in one revolution is the circumference of the circle.**

So,

Given,

**Speed of an object moving is circular path is define as the ratio of distance travelled in one revolution to the time taken by the object to complete one revolution.**

Let be the speed of the ball.

So,the speed of the ball is

**Answer:**

correct is b 7N

**Explanation:**

The torque is

Στ = I α

torque

**τ** =** F** x** R**

bold, indicate vectors. The magnitude of torque is

τ = F R sin θ

in this case the angle is 90º so sin 90 = 1

τ = F R

The moment of inertia of a cylinder

I = ½ M R²

substitute

F R = ½ M R² α

F = ½ M R α

reduce to the SI system

R = 7 cm (1m / 100cm) = 0.07 m

calculate

F = ½ 2 0.07 100

F = 7 N