Chapter 7

 Vertical (y)  Horizontal (x)  When solving a projectile problem, you can’t mix vertical and horizontal information in the same formula

 A projectile launched horizontally (would this be the x or y direction?) has no initial vertical motion. This means v 0y = 0 m/s  Gravity/acceleration for falling objects (on Earth) is still -9.8 m/s 2  Starting distances and times are still 0

 A stone is thrown horizontally at a speed of 5.0 m/s from the top of a cliff 78.4 m high. a. How long does it take the stone to reach the bottom of the cliff? b. How far from the base of the cliff does the stone hit the ground?

 Draw a picture and label known information  Think of the problems as consisting of 2 parts; horizontal and vertical  Vertical motion is just like free-fall (gravity is acceleration)  Horizontal motion is just like the chapter 5 problems  The time from launch to hitting the ground is the same for both horizontal and vertical motion. You only solve for time once!

 Draw and label

 Group your information – either horizontal or vertical (x or y)

 If you don’t have time, solve for it. Remember, time can be used for both horizontal or vertical motion.  Which formula should you use?

 d = d 0 + v 0 t + ½ at 2  78.4 = ½ (-9.8)t 2  t 2 = 16  t = ?

 Which formula?

 d = d 0 + vt  d = 0 + 5(4)  d = ?

 20 m