Solving Word Problems

1
Solving Word Problems

• To solve a word problem, think
• numbers, question, formula, label
• circle the numbers, read the question, write the
  formula and finally label the parts of the
  question that relate to the formula

2
Solving Word Problems contd

• Lets do a sample for density follow the
  prompts
• A sample of substance X has a density of 5 g/ml
  and a mass of 80 g. What is its volume?
• --------------------------------------------------
  --------------
• numbers
• question
• formula
• label
• Then, solve the equation. Volume 80 g / 5
  g/ml
• Volume 16 ml

density
mass
Density Mass / Volume
Volume Mass / Density
3
MOTION

• Describing How Things Move

4
Motion

• Also called Kinematics
• Measured as a change in position
• Distances can be positive or negative
• Depends on the frame of reference

5
Frame of Reference

• Described by the observer
• Compares speeds and angles to the observers
  surroundings
• Explains the 75mph fly

6
Speed

• How rapidly an object changes location
• Described in units of distance divided by units
  of time
• Miles per hour
• Kilometers per hour
• Centimeters per month

7
Speed Formula
d distance

• V
• speed

t time
d distance
V speed
t time
8
What is the speed of a runner that travels 250m
in 50min.?

1. 5 m/min.
2. 0.2 m/min.
3. 12,500 m/min.

9
How long does a trip of 3000 km take if you
travel at 110 km/hr.?

1. 330000 hr.
2. 0.037 hr.
3. 27 hr.

10
How far will a car traveling at 70km/hr. go in 2
hours?

1. 360 km
2. 140 km
3. 0.4 km
4. 2.5 km
5. 0.04 km

11
Average human walking speed is 5 km/hr. How far
can you walk in two hours?

1. 10 km
2. 10 km/hr.
3. 10 hr.
4. 10 kmhr.
5. None of the above

12
What is the speed of a bike that travels 12 km in
30 min.?

1. 360 km/hr
2. 24 km/hr
3. 0.4 km/hr
4. 2.5 km/hr
5. 0.04 km/hr

13
Three Kinds of Speed
14
Speed

• What is the average speed of a cheetah that
  sprints 100 m in 4 s?
• How about if it sprints 50 m in 2 s?
• 2) If a car moves with an average speed of 60
  km/h for an hour, it will travel a distance of 60
  km.
• (a) how far would it travel if it moved at
  this rate for 4 h?
• (b) for 10 h?

15
Speed 2

• 3) In addition to speedometer on the dashboard of
  every car is an odometer, which records the
  distance traveled. If the initial reading is set
  at zero at the beginning of a trip and the
  reading is 40 km one half hour later, what has
  been your average speed?
• 4) Would it be possible to attain the average
  speed in previous example and never go faster
  than 80 km/h?

16
Velocity
Velocity describes the speed and the direction of
motion
17
Instantaneous Velocity
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Speed or Velocity?

• 186,282 mi. / s
• 107 km / h North
• 55 mi. / h
• 1300 km / h East
• 212 mi. / h

19
Velocity

• With what is the race-car driver concerned, speed
  or velocity?
• The speedometer of a car moving to the east reads
  100 km/h. It passes another car that moves to the
  west at 100 km/h. Do both cars have the same
  speed?
• Do they have the same velocity?
• During certain period of time, the speedometer of
  a car reads a constant 60 km/h. Does this
  indicate a constant speed or a constant velocity?

20
Velocity

• How might you estimate your speed if the
  speedometer in your car is broken?
• Which of the following can be used to measure an
  average speed stopwatch, odometer, or
  speedometer?
• An instantaneous speed?