Motion in One Dimension Notes and Example Problems
t = time in seconds x= horizontal distance in meters y = vertical distance in meters v i = the initial velocity in m/s v f = the final velocity in m/s a = acceleration in m/s 2
Acceleration of Gravity If an object is falling towards the earth surface then you use g or a g = -9.81 m/s 2. *This means that an object speeds up 9.8 m/s every second. *It is negative because objects fall downward. If the object is simply moving, use normal equations to solve for displacement and acceleration.
v av = x t a = (v f -v i ) t y = v i t + ½ a t 2 y or x, depending on what direction the object is accelerating x = ½(v i + v f ) t v f = v i + a t v f 2 = v i 2 + 2a x
Problem Solving Tips Anything going down is Object starting from rest Object that is stopping Object at its peak when thrown up When dropping an object, we know Time up = time down in vertical displacement
Problem Set-Up Given: t = 0.53s not stated, but still there v i = 0 m/s a = -9.8 m/s 2 Unknown: y Equation: y = v i t + 1/2 a t 2
Solution v i = 0 m/s so y = v i t + 1/2 a t 2 since v i = 0 y = 1/2 a t 2 y = 1/2 (-9.8 m/s 2 )(0.53s) 2 y = -1.376 m (falling down) So the table is approximately 1.4 meters high.
Tom needs to get away from a bomb that Jerry has set. If he uniformly accelerates from rest at a rate of 1.5 m/s 2, what will his final velocity be when he gets 25 meters away?
Tom and Jerry Problem Set-Up Given: v i = 0 m/s x= 25 m a = 1.5 m/s 2 Unknown: v f Equation: v f 2 = v i 2 + 2a x
Tom and Jerry Problem Solution v f 2 = v i 2 + 2a x v f 2 = (0 m/s) 2 + 2(1.5 m/s 2 )(25 m) v f 2 = 75 m 2 /s 2 v f = 8.7 m/s Tom will be traveling at 8.7 m/s.
Road Runner Problem Set-Up Given: v i = 0 m/s a= -9.8 m/s 2 t = 3.5 s Unknown: v f and y Equation: a = (v f - v i )/ t
Road Runner Problem Solution PART a) a = (v f -v i )/ t but v i = 0 m/s so (-9.8 m/s 2 ) = (v f - 0 m/s)/ 3.5 s (-9.8 m/s 2 ) = v f / 3.5 s = -34.3 m/s The piano will hit the ground at a speed of -34 m/s, neglecting the affects of air resistance of course.
Road Runner Problem Solution PART b) Unknown: y Equation: y = v i t + 1/2 a t 2
Road Runner Problem Solution PART b) y = v i t + 1/2 a t 2 but v i = 0 m/s so y = 1/2 a t 2 = 1/2 (-9.8 m/s 2 )(3.5 s) 2 = -60.025 m The piano fell 60. meters.