The speed of a moving bullet can be deter-
mined by allowing the bullet to pass through
two rotating paper disks mounted a distance
81 cm apart on the same axle. from the
angular displacement 13.7° of the two bul-
let holes in the disks and the rotational speed
432 rev/min of the disks, we can determine
the speed of the bullet.

Explanation:

Rotational Motion

An object is said to have rotational motion is it moves at the same distance to a fixed point called the center. The distance is called radio and the number of revolutions (or radians) it makes over time is called angular speed. Knowing the angle it makes in a certain time t, the angular speed is

If we wanted to know the time it takes to describe some angle, we solve for t

Two rotating paper disks are mounted at a distance of x= 81 cm = 0.81 m. If we knew the time the bullet take from one to the other, we could determine the speed of the bullet

We can determine the time taken between the disks knowing their angular speed and the angle formed in the interval. Replacing the time from [1] into [2]

We have the values

Thus

b. lifting dumbbell weight at 20-degree angle from the body after a 45-degree angle