Kinematics concepts3UB PHYSICS

Average Speed twistA car travels 1.0 km through a town at 50.0 km/h and

then drives 1.0 km through the country at 100.0 km/h. What is the average speed of this car?

v = Δd/Δt= total distance/total timeWe need the time for each section of the motion!

Average Speed twistt1 = d1/v1

= 1.0 km/50.0 km/h = 0.020h

t2 = d2/v2 = 1.0 km/100.0km/h

= 0.010h

Average Speed twistv = (1.0 + 1.0)km/(0.020 + 0.010)h

= 67 km/h

Note: This average speed is NOT the average of 100 km/h and 50 km/h. Why?

Graphing this questionThe car drove 1.0 km at 50 km/h in 0.20 h and then

1.0 km at 100 km/h for 0.10 h. The average speed we found was 67 km/h. The two motions are each UM:

UM question 1The following graph shows the Northward motion

of a wolf tracking a biology teacher.

UM question 1

A) What is the wolf’s position at 4.0 s?b) What is the wolf’s displacement

between 2.0 s and 8.0 s?c) What is the velocity of the wolf?

UM question 1a) 4.0 m [N]b)Δd =df-di= 8.0 m [N] – 2.0 m [N] = 6.0 m [N]c) v = Δd/Δt =(10m[N] – 0)/(10s – 0) = 1.0m/s [N

UM question 2The motion of a biology teacher heading North

during migration season. The origin represents a town he passes through.

UM question 2a) What is the total displacement?b) What is the total distance traveled?c) What is the total displacement from the town?d) At what time does the migrating dude reach the

town?e) Where does he start?f) What is his average velocity?

UM question 2a) Δd = df-di= 60 km – (-40 km) = 100 km [N]b) Δd = 100 kmc) Δd from town = 60 km [N]d) Δt = 4 he) He starts 40 km [S] of town.f) v = Δd/Δt = (60 km – 0)/(10 h – 4 h) = 10 km/h [N]

UM Problem 3An aimless chemistry teacher wanders as:

UM Problem 3Notice that we must label displacement rather

than distance; why?The slopes for each line segment, yields the

velocity for that time interval. Find each.Describe the motion of the above graph.What section shows the highest velocity?Which section shows the greatest displacement?

Find Δd for each section.What is the total displacement of the object?

Displacement and distance from v-t graphs.For motion comprised of UM and UAM, we will need

to find the total distance and displacement by adding the areas up.

Displacement and distance from v-t graphs. The total distance is found by adding areas. The total displacement is found by adding areas above the x-

axis and adding negative areas below the x-axis. Break up the graph into a series of triangles and rectangles

to find the distance or displacement at certain times. (Useful info if asked to plot a d-t graph for the same motion!)

In this question, find: distance, displacement, speed and velocity.

Sketch the distance and displacement versus time graphs