Transcript A.P. Physics B

A.P. Physics B
6.5 #’s 2-4
By: Anna Findley
6.5 # 2
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2. [CJ5 6.P.036.] A 47.0 g golf ball is driven from
the tee with an initial speed of 52.0 m/s and rises
to a height of 24.6 m.
(a) Neglect air resistance and determine the kinetic
energy of the ball at its highest point.
(b) What is its speed when it is 8.0 m below its
highest point?
Solution Part A
(a) Neglect air resistance and determine the
kinetic energy of the ball at its highest
point.
 KE + mgh=½ mv2
 KE+ (.047kg) (9.8) (24.6m) = ½ (.047kg)
(52.0m/s) 2
 KE= 52.2 J
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Solution Part B
(b) What is its speed when it is 8.0 m below
its highest point?
 KE + mgh = ½mv2 + mg (h-8.0)
 (52.2J) + (.047kg) (9.8) (24.6m) =
½(.047kg) v 2 + (.047kg) (9.8) (16.6m)
 V= 48.77m/s
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6.5 # 3
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3. [CJ5 6.P.037.] A cyclist approaches the
bottom of a gradual hill at a speed of 11
m/s. The hill is 5.0 m high, and the cyclist
estimates that she is going fast enough to
coast up and over it without peddling.
Ignoring air resistance and friction, find the
speed at which the cyclist crests the hill.
Solution #3
KE + PE = KE + PE
 ½ mv2+ mgh = ½ mv2+ mg
 (½)(112) + 0 = (½)(v2) + (9.8)(5)
 V = 4.8 m/s
 Remember: mass cancels out...
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6.5 # 4
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*4. [CJ5 6.P.041.] A water slide is
constructed so that swimmers, starting from
rest at the top of the slide, leave the end of
the slide traveling horizontally. As the
drawing shows, one person hits the water
5.00 m from the end of the slide in a time of
0.500 s after leaving the slide. Ignoring
friction and air resistance, find the height H
in the drawing.
Solution # 4
Vx= d/t
 Vx= (5.00m) / (0.500s)
 Vx= 10.0 m/s
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Vfy = Viy + at
 Vfy = 0 + (9.8) (0.500s)
 Vfy = (4.9m/s)
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Solution # 4 Continued
Use the Pythagorean Theorem to find Vf
 Vx2 + Vfy2 = vf2
 Vf = 11.14
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Vf2= 2ad
 11.142 = 2 (9.8) d
 D = 6.33
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