1 Problem 4, page 50

1
(1) Problem 4, page 50

• (a) A bristlecone pine tree has been known to
  take 4000 years to grow to a height of 20 ft.
  Find the average speed of growth in m/s. (b) In
  contrast, the fastest growing plant is the giant
  kelp, which can grow at a rate of 2 feet in one
  day. Find the average speed of growth of this
  plant in m/s.

2
Solution Prob. 4 (a)
3
Solution Prob. 4 (b)
4
(2) Problem 26, page 51

• A truck covers 40.0 m in 8.50 s while smoothly
  slowing down to final speed of 2.80 m/s. (a) Find
  its original speed. (b) Find its acceleration.

x
xf 40.0 m
xi 0 m
5
Solution Prob. 26
vxo and ax are two unknowns in this problem.
Apply the two kinematics equation, eliminate
axand then solve for vxo.
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Solution Prob. 26 cont
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Solution Prob. 26 part (b)
Use answer from part (a)
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(3) Problem 46, page 52

• A peregrine falcon dives at a pigeon. The falcon
  starts downward from rest and falls with
  free-fall acceleration. If the pigeon is 76.0 m
  below the initial position of the falcon, how
  long does it take the falcon to reach the pigeon?
  Assume that the pigeon remains at rest.

9
Solution Prob. 46
y
x
vyo 0
yi 76.0 m
peregrine
vf ?
yf 0 m
pigeon
10
Solution Prob. 46
y
x
vyo 0
yi 76.0 m
peregrine
Time is the unknown algebraically solve for t.
vf ?
yf 0 m
pigeon
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(4) Problem 66, page 53

• Another scheme to catch the roadrunner has
  failed. A safe falls from rest from the top of a
  25.0 m high cliff toward Wile E. Coyote, who is
  standing at the base. Wile first notices the safe
  after it has fallen 15.0 m. How long does he have
  to get out of the way?

12
Solution Prob. 66
y
x
yi 25.0 m
vyo 0
vyf1 ?
yf1 15.0 m
Wile
vyf2 ?
yf2 0 m
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Solution Prob. 66 cont

• Method of solving
• Step 1. Find the time it takes the safe to fall
  10.0 m, thats the height Wile first notices the
  safe.
• Step 2. Find the time it takes the safe to fall
  25.0 m.
• Step 3. The difference in time between step 2 and
  step 1 time Wile has to get out of the way.

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Solution Prob. 66 cont
Step 1
Step 2
Step 3