Solving Word Problems

Solving Word ProblemsTo solve a word problem, think:

numbers, question, formula, labelcircle the numbers, read the question,

write the formula and finally label the parts of the question that relate to the formula

Solving Word Problems – cont’dLet’s do a sample for density – follow the promptsA sample of substance X has a density of 5 g/ml

and a mass of 80 g. What is it’s volume?----------------------------------------------------------------numbersquestion formulalabelThen, solve the equation. Volume = 80 g / 5

g/mlVolume = 16 ml

Density = Mass / Volume Volume = Mass / Density

massdensity

Unit 4 – Lecture 1

MotionKinematics – branch of science which

describes motion [without describing the cause of the motion]

motion is measured as a change in positiondistances can be positive or negative

depends on the frame of reference

Frame of Referencethe frame of reference depends on the

observercompares speed and angles of movement

from the observer’s perspective and surroundings

explains the 75mph fly

SpeedSpeed – how rapidly an object changes

locationunits of distance divided by units of time

ex: miles per hour, kilometers per hour, centimeters per month, etc. d

distance

V

speed

t

time

Vspeed

=

d

distance

t

time

PracticeWhat is the speed of a runner that travels 250 m in 50 min?

5 m/min. 0.2 m/min. 12,500 m/min.How long does a trip of 3000 km take if you travel at 110 km/hr.?

330000 hr. 0.037 hr. ~27 hr.How far will a car traveling at 70km/hr. go in 2 hours?

360 km 140 km 0.4 km 2.5 km 0.04 kmWhat is the speed of a bike that travels 12 km in 30 min.?

360 km/hr 24 km/hr 0.4 km/hr 2.5 km/hr 0.04 km/hrAverage human walking speed is 5 km/hr. How far can you walk in

two hours?10 km 10 km/hr. 10 hr. 10 km•hr. [none]

Types of SpeedThree types of speed [distance divided by time]

average speedtotal distance divided by total time

instantaneous speedhow fast you’re going NOW

constant speedspeed that does not changenot really observed on earth – objects in

orbit, etc.

More PracticeWhat is the average speed of a cheetah that

sprints 100 m in 4 s?How about if it sprints 50 m in 2 s?

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?

25 meters / second

25 meters / second

240 km

600 km

More Practice – cont’dIn 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?

Would it be possible to attain the average speed in previous example and never go faster than 80 km/h?

80 kilometers per hour

No – in order to have an average, need to have speeds higher and lower . If you had a constant speed, this would work, however, that is not realistic for typical scenarios.

Velocity describes the speed AND the direction of an object’s motion.

Types of Velocity

Speed or Velocity?186,282 mi. / s107 km / h North55 mi. / h1300 km / h East212 mi. / h

PracticeWhich is a race car driver concerned with –

speed or velocity? a drag racer?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 both cars 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?

velocity [curved path]speed [going straight]

yes

no

constant speed – if it were velocity, there would be a direction listed

More PracticeHow might you estimate your speed if the

speedometer in your car is broken?

Once more, explain the difference between speed and velocity to a partner.

[various]