A.P. Physics B

1
A.P. Physics B

• 6.5 s 2-4
• By Anna Findley

2
6.5 2

• 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?

3
Solution Part A

• (a) Neglect air resistance and determine the
  kinetic energy of the ball at its highest point.
• KE mgh½ mv2
• KE (.047kg) (9.8) (24.6m) ½ (.047kg)
  (52.0m/s) 2
• KE 52.2 J

4
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

5
6.5 3

• 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.

6
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...

7
6.5 4

• 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.

8
Solution 4

• Vx d/t
• Vx (5.00m) / (0.500s)
• Vx 10.0 m/s
• Vfy Viy at
• Vfy 0 (9.8) (0.500s)
• Vfy (4.9m/s)

9
Solution 4 Continued

• Use the Pythagorean Theorem to find Vf
• Vx2 Vfy2 vf2
• Vf 11.14
• Vf2 2ad
• 11.142 2 (9.8) d
• D 6.33