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B. Free fall - falling where the only force is gravity (no friction)

1. Free fall Word Problems

Use same method and equations as before …

… except always remember when you read...

…an object is dropped: 

  You Know …

V_i = 0

a = g = +9.8m/s²
(make down +)

… an object is ascending:

a = g = -9.8 m/s²
(make down -)

 
a. Simple Freefall problems

 Ex) A coin is dropped in a vacuum tube, find its displacement after .3 seconds.

 
Step 1 - Read and underline all the important information

 Ex) A coin is dropped in a vacuum tube, find its displacement after .3 seconds.

Step 2 - Turn all your information into letters

 
V_i = 0   (Object is dropped)
a = +10 m/s²
d = ?
t = .3 seconds

 
Step 3 -  Substitute and Solve

d = V_it + 1/2at² 

d = 0 m/s(.3 sec) + 1/2(+10 m/s²)(.3 sec)²

Answer:  d = .45 m

Ex) Find the coin's velocity after .3 seconds

Search the Mechanics Section on the equation sheet to find the equation that fits
 

Ex) Find the coin's velocity after .3 seconds

V_f = ?
t = .3 seconds
a = g = 9.8 m/s² (falling)
V_i = 0 m/s

 
a = (V_f - V_i)/ t

V_f = 2.94 m/s
 

Ex) A rocket is fired vertically upward with an initial velocity of 29 m/s .

When the rocket reaches its maximum altitude it has a velocity of 0 m/s. 
Find the rocket's maximum altitude.

Ex) A rocket is fired vertically upward with an initial velocity of 29 m/s . When the rocket reaches its maximum altitude it has a velocity of 0 m/s. 

Find the rocket's maximum altitude.

Altitude??

V_i = +29 m/s

V_f = 0 m/s
a = g = -9.8 m/s²

d = ?

 V_f² = V_i² + 2ad

Answer: 42.9 m

V_i= 0 m
d = 64 m
t = 4 sec
a = ?

d = V_it + 1/2 at²

64 m = 0 m/s(4 sec) + 1/2a(4 sec)²

a = 8 m/s²