PHYSICS LAB HOMEWORK
Ali7
HW: Motion in Two Dimensions Name Section
Copyright 2008 by S. Kanim, M. Loverude, & L. Gomez 1
1. In lab you took a photograph of a toy roller coaster cart as it rolled along a track and then flew through the air and into a bucket. The diagram from lab is reproduced here. You will use your photograph from the lab to answer the questions below.
i. Use the light stripes in the photograph to find the change in velocity vector for the coaster for a
portion of the path when it is at the straight part of the track. (Somewhere near point A in the diagram.) Find and measure two adjacent light stripes near this point and show them below. (Be sure to keep their directions – you may want to use a protractor.) Label these vectors as initial velocity and final velocity or vi and vf. Then find the change in velocity vector as you did in lab. Show your work. Finally, draw an arrow to represent the direction of acceleration for this interval.
ii. Repeat part i. for two adjacent stripes near the bottom of the track, somewhere near point B. iii. Repeat part i. for two adjacent stripes after launch but before the cart has reached its highest point
while in flight, somewhere near point C. iv. Repeat part i. for two adjacent stripes near the highest point while in flight, somewhere near point D. v. Repeat part i. for two adjacent stripes after the highest point while in flight, somewhere near point E.
A
B
C
D
E
Catch
bucket
Coaster
HW: Motion in Two Dimensions
Copyright 2008 by S. Kanim, M. Loverude, & L. Gomez 2
2. For each pair of vectors shown below, use a ruler (and protractor if necessary) to perform the indicated subtraction as shown in the example.
A
r
B
r
C= B– A
r r r –A
r
B
r C
r
Example
E
r
F
r
D= E –F
r r r
i.
H
r
I
r G= H – I
r r r
ii.
L
r
J= K – L
r r r
iii.
K
r
3. A car is speeding up (but not turning left or right) as it passes over the crest of a hill as shown. Indicate the approximate direction of the acceleration of the car for the time that it travels between points A and B. Show how you determined your answer.
A
B
HW: Motion in Two Dimensions
Copyright 2008 by S. Kanim, M. Loverude, & L. Gomez 3
4. In each case i. through v. below, find the change in velocity vector ! r v from the initial point to the final
point for an object moving along the path shown. Indicate ! r v with a dashed line vector, and graphically
determine its magnitude. Use a scale 1 centimeter = 1 meter per second. In the space to the right of each case, draw an arrow that shows the direction of the average acceleration for the time that the object travels from the initial to the final point.
{Recall that the average acceleration is defined by the vector equation
r a ave =
! r v
!t . Since Δt is a scalar, the
direction of
r a ave must be the same as the direction of !
r v .}
v = 4 m/s r
-v i
r
Example Initial:
v = 4 m/s rFinal:
v f
r
!v = 0 r
v = 4 m/s r
i. Initial:
v = 5 m/s rFinal:
v = 4 m/s rInitial:
v = 3 m/s rFinal:
!v = r
v = 4 m/s rInitial:
v = 4 m/s rFinal:
v = 4 m/s rInitial:
v = 3 m/s rFinal:
v = 4 m/s rInitial:
v = 0 rFinal:
ii.
iv.
v.
!v = r
!v = r
Acceleration direction:
Acceleration direction:
Acceleration direction:
Acceleration direction:
None.
!v = r Acceleration direction:
iii. !v = r Acceleration direction:
HW: Motion in Two Dimensions
Copyright 2008 by S. Kanim, M. Loverude, & L. Gomez 4
5. A toy car with a blinkie attached moves in a clockwise direction around a racetrack. A drawing of the trail made by the blinkie is shown. The car starts at rest from point A. By the time it reaches point D it is traveling at a constant speed, and continues at this speed until it reaches point G. It then slows down to a stop. i. On the diagram at right, draw velocity vectors
for each of the points A – G. Be sure that the relative magnitudes of your vectors are consistent.
ii. Now draw the change in velocity vectors for
each of the points A – G. Use the light stripes just before and just after each point to find initial and final velocities. An example is shown for point C.
iii. Based on your answer to part ii., draw
acceleration vectors for each point. iv. How does the magnitude of the acceleration at point E compare to that at G? Explain.
A B
C
DE
F
G
A B
C
DE
F
G
vf r
A B
C
DE
F
G
vi r
vf r
–vi r
C
!v r