Physics 111

1-D Motion
the average velocity is
non-zero over some time
interval, does this mean
that the instantaneous
velocity in never zero
during the same interval?
1. Yes
2. no
instantaneous can 0 or
negative for a time, but the
average can still be zero
Example: 6+2+9+0 (meters) /
4sec = 4.25
 What
is given and what do we need to find?
 How do we decide what equation to use?
final = v initial + a(t)
 Vf= 50
 Vi=20
 A= 4.2
 WANT t =???
50 = 20 + 4.2(t)
T= 7.1 seconds
 Soh-Cah-Toa
 Fred
is practicing shooting at the range. Fred
is standing 50 meters away from his target.
When Fred shoots at an angle of 10 degrees,
he hits the bottom of the target, but then
when he shots at an angle of 4 degrees, he
hits the top of the target. At what angle does
he have to shoot to hit the middle of the
target, if the target is a square.
 (HINT: Draw a picture)
Find the height of both shots
 Subtract them to get the height of the target
 Divide in half to get the middle hieght
 Plug answer and adjacent back into tan
function to find the angle
 (Answer and process in previous lecture)
 You
throw a ball upward with an
initial speed of 10 m/s. Assuming
that there is no air resistance, what
is its speed when it returns to you?
A. More than 10 m/s
B. 10 m/s
C. Less than 10 m/s
D. zero
 Since acceleration is gravity
and is the same on the way up
and down, the ball will return
to the same velocity
 You
drop a rock off of a bridge.
When the rock has fallen 4 m, you
drop a second rock. As the two rocks
continue to fall, what happens to
their separation?
a) Separation increases as they fall
b) Separation stay constant
c) Separation decreases
 The
separation increases as they fall
 Why??
 They increase at the same
acceleration, but do not have the
same velocity
 The first rock will always have a
greater velocity than the second,
and the distance in-between will
 You
toss a ball
straight up in the
air and catch it
again. What graph
represents this?
 You
drop a very bouncy ball. It falls,
and then it hits the floor and
bounces right back up to you. Which
graph represents this?
 You
drop the ball and it leaves your hand,
but doesn’t hit the floor.
 What graph is this?
accidently drop your curly
fries while walking to your
table. Your fries fall halfway to
the group in .7 seconds. How
much time do you left to try to
save your fries?
 Used to find the height
 Delta X 1/2= 0(.7)- .5(9.8)(.7)^2
 X 1/2= height = 2.401 m *2 = 4.8 m
Plug delta Hs into equation
 4.8 = 0 - .5(9.8)(t)^2
 Ttotal = 1 second
 Ttotal = t first half + t second half
 1-.7 = t second half
 =.3
for second half of fall
(Can’t use 2.4 for the X initial because we
don’t know its initial velocity at .7 seconds)
Chuck is riding the Giant
Drop at Great America. If Upton
free falls for 2.60 seconds, what
will be his final velocity and how
far will he fall?
 Time
 Initial velocity
Need to find:
Distance and Final Velocity
Use: Delta x = Vi*t + .5(9.8)(2.60)^2
Distance = 33.1 m
Plug into V final = V initial + a(t)
Vfinal = 25.5 m/s
bullet is moving at a speed of 367 m/s
when it embeds into a lump of moist clay.
The bullet penetrates for a distance of
0.0621 m. Determine the acceleration of the
bullet while moving into the clay. (Assume a
uniform acceleration.)
 Given:
 vi
= 367 m/s
 vf = 0 m/s
 d = 0.0621 m
Find acceleration
Use: vf2 = vi2 + 2*a*d
(0 m/s)2 = (367 m/s)2 + 2*(a)*(0.0621 m)
A= -1.08*10^6 m/s^2
(- means deacceleration, slowing down)