Solving Problems Using Motion equations

Inside Out Bubble - Stony Brook University

Dr. Helio Takai

Water on the inside, Air on the Outside

E. Solving Problems using the motion equations

Ex 3) Starting from rest, an object accelerates at a rate of 12 m/s². What is the velocity of the object at the end of 3.0 seconds?

Problem Solving Steps

• Step 1 - Read for information

• Step 2 - List information

• Step 3 - Plug in and Solve

Ex 3) Starting from rest, an object accelerates at a rate of 12 m/s². What is the velocity of the object at the end of 3 seconds?

V_i = 0 (Starting from rest)

a = 12 m/s²

V_f = ?

t = 3.0 seconds

a = (V_f - V_i)/t

12 m/s² = (V_f - 0)/3.0 secs

(Cross Multiply and Solve)

V_f = 36 m/s

Ex 4) An object at 100. m/s accelerates at a rate of 120. m/s². What will the velocity of this object be after .10 seconds?

Underline Info

Ex 4) An object at 100. m/s accelerates at a rate of 120. m/s². What will the velocity of this object be after .100 seconds?

a = (V_f - V_i)/t

120. m/s²= (V_f - 100. m/s)/.100 s

• Cross Multiply

12.0 = (V_f - 100.)

V_f = 112 m/s

3 ways to have non-zero acceleration

(to change velocity):

• Speed Up

• Slow Down

• Change Direction

F. Motion Terms and Direction

A whole branch of mathematics is required to deal with numbers that have direction

Trigonometry

This is why it is important to know which motion information has direction

Vector - a quantity that includes magnitude (a number) & direction

ex) displacement, acceleration, velocity

Scalar - a quantity that includes magnitude (a number) only

ex. time, distance, speed