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Unformatted text preview: = tr − 0 + i .
2a v 0
v0
v0 (b) With si = 16 m , v 0 = 60 k m h , a = − 2.0 m s 2 , and t r = 1.1 s ,
t light = 1.1 s − 2.43 ⎛ 0.278 m s ⎞
16 m ⎛ 1 k m h ⎞
⎜ 1 k m h ⎠ + 60 k m h ⎝ 0.278 m s ⎠ = 6.2 s .
⎟
⎜
⎟
2 − 2 .0 m s ⎝ ( 60 k m h 2 ) (a) From v 2 = v i2 + 2a( ∆y ) with v f = 0 , we have
f ( ∆y )max = v 2 − v i2
f
2a = 0 − ( 25.0 m s ) ( 2 −9.80 m s 2 2 ) = 31.9 m . (b) The time to reach the highest point is t up = v f − vi
a = 0 − 25.0 m s
= 2.55 s .
− 9.80 m s 2 (c) The time required for the ball to fall 31.9 m, starting from rest, is found from 2 ( ∆y )
2 ( − 39.1 m )
1
=
= 2.55 s .
∆y = ( 0) t + at 2 as t =
− 9.80 m s 2
a
2 (d) The velocity of the ball when it returns to the original level (2.55 s after it starts to fall
from rest) is ( ) v f = v i + at = 0 + − 9.80 m s 2 ( 2 .55 s ) = − 25.0 m s . 35 CHAPTER 2.44 From v 2 = v i2 + 2a( ∆y ) , with v i = 0, v f = 29 000 km h , a n d ∆y = + 18 m ,
f ( ⎡ 2.9 × 10 4 k m h
a=
=⎣
2 ( ∆y )
2 (18 m )
v 2 − v i2
f 2.45 2 ) 2 − 0 ⎤ ⎛ 0.278 m s ⎞ 2
6
2
⎦
⎜ 1 k m h ⎟ = 1.8 × 10 m s .
⎝
⎠ Assume the whales are traveling straight upward as they leave the water. Then
v 2 = v i2 + 2 a( ∆y ) , with v f = 0 w h en ∆y = + 7.5 m , gives
f ( ) v i = v 2 − 2 a( ∆y ) = 0 − 2 −9.8 m s 2 ( 7.5 m ) = 12 m s .
f 2.46 1
Use ∆y = v i t + at 2 , w ith v i = 0, a = −9.80 m s 2 , a n d ∆y = −76.0 m to find
2
t= 2.47 2 ( ∆y ) a = 2 ( − 76.0 m )
−9.80 m s 2 = 3.94 s . (a) After 2 .00 s , the velocity of the mailbag is (v )
f bag ( ) = v i + at = −1.50 m s + −9.80 m s 2 ( 2 .00 s ) = − 21.1 m s . The negative sign tells that the bag is moving downward and the magnitude of the
velocity gives the speed as 21.1 m s
(b) The displacement of the mailbag after 2 .00 s is ⎡ −21.1 m s + ( −1.50 m s ) ⎤
⎛ v f + vi ⎞
t=⎢
⎥ ( 2.00 s ) = − 22.6 m .
2⎟
2
⎠
⎢
⎥
⎣
⎦ ( ∆y )bag = ⎜
⎝ During this time, the helicopter, moving downward...
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This note was uploaded on 03/03/2010 for the course PHY P221 taught by Professor Dr.ha during the Spring '05 term at Indiana University South Bend.
 Spring '05
 Dr.Ha
 Physics, Acceleration

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