Chapter N4

1
Chapter N4

• Motion from forces
• Due Friday N4.B1, B2, B.7, B.8

2
These are graphs showing the motion of a car
along a straight road. Explain what is happening
to the displacement, the velocity and the
acceleration of the car.
r
v
a
t
3
Problems for the groups

• When your group has the curves drawn, draw them
  on the board.
• Case 1. An object is shot straight into the air
  and falls back (like the balls you shot in the
  air). t0 vv0 when the ball leaves the gun.
  Draw the curve until the ball comes back to the
  starting point.
• Case 2. A rocket is shot straight in the air
  with an engine that burns for 4 seconds with an
  acceleration of 20 m/s2. It then falls back to
  earth.
• As soon as you are ready put them on the board.
• The first group done with both problems gets 5
  bonus points.
• A group that successfully points out problems
  with another groups answer receives 2 bonus
  points.

4
Problems

• Case 1. An object is thrown straight into the
  air and falls back. t0 when the object leaves
  the hand which happens at y 0. Draw the curve
  until the object comes back to the starting
  point.
• Case 2. A rocket is shot straight in the air
  with an engine that burns for 4 seconds. It then
  falls back to earth.

5
Equations for your formula sheet
Similar equations exist for y, and z.
Use the x, y, or z equations depending on the
direction of the force (acceleration).
Often this will be the vertical direction and the
acceleration will be g.
6
Sample problem A car starts from rest and
accelerates (2m/s2) for 5 seconds. What are the
velocity and position of the car at that time?

• List the data on your paper, raise your hand when
  you are done. 6
• x00, v00, a2 m/s2, t 5 sec, v ?, x ?.

v10m/s x25m
7
An object is dropped starting from rest from a
height of 25 m. Find the position and velocity
of the object at the end of 2.2 s.

• Write the data. Raise your hand when done.
• y025 m, v00, a -9.8 m/s2, t 2.2 s, v ?, y
  ?

v - 9.6 m/s y 23.7 m
How long will it take the ball to strike the
ground?
t 2.26 s
8
An object thrown straight up from a height of 25
m with a velocity of 12 m/s. Find the position
and velocity of the object at the end of 2.2 s.

• Write the data. Raise your hand when done.
• y025 m, v012 m/s, a -9.8 m/s2, t 2.2 s, y
  ?, vy?

v - 9.6 m/s m/s y -23.7 26.4 25 m 27.7 m
t 3.8 s
9
A ball is thrown straight into the air and takes
3 seconds to fall back to the ground.

• What is the maximum height of the ball and with
  what velocity was it thrown into the air?
• Write the data.
• Write the equation to find the velocity with
  which it was thrown.
• Find the velocity.
• Write the equation to find the height.
• Find the height.

v 14.7 m/s
y 11 m
10
Problems due Friday

• N4.B1, B2, B.7, B.8