# A rifle is aimed horizontally toward the center of a target 100m away. If the bullet strikes 10cm below the center, what was the velocity of the bullet?

Solution:

#### Vx = ∆x/∆t = (100) / (0.143) = 700.001 m/s

This problem uses the independence of horizontal and vertical movements. There is no horizontal acceleration in free flight, and the vertical acceleration is always g = -9.8 m/s>sup>2.

One of the powers of physics is its ability to use physics principles to make predictions about the final outcome of a moving object. Such predictions are made through the application of physical principles and mathematical formulas to a given set of initial conditions.

In the case of projectiles, a student of physics can use information about the initial velocity and position of a projectile to predict such things as how much time the projectile is in the air and how far the projectile will go.

The mathematical formulas that are used are commonly referred to as kinematic equations. Combining the two allows one to make predictions concerning the motion of a projectile.

In a typical physics class, the predictive ability of the principles and formulas are most often demonstrated in word story problems known as projectile problems.