This preview shows page 1. Sign up to view the full content.
Unformatted text preview: with constant velocity,
undergoes a displacement of ( ∆y )copter = vi t + 2 at 2 = ( −1.5 m s ) ( 2.00 s ) + 0 = − 3.00 m .
1 During this 2 .00 s , both the mailbag and the helicopter are moving downward. At
the end, the mailbag is 22 .6 m − 3.00 m = 19.6 m below the helicopter. 36 CHAPTER 2 (c) Here, ( v i )bag = ( v i ) copt er = + 1.50 m s and abag = −9.80 m s 2 while acopter = 0 . After
2.00 s , the speed of the mailbag is (v )
f bag = 1.50 m
m⎛
m⎞
m
+ ⎜ −9.80 2 ⎟ ( 2.00 s ) = − 18.1
= 18.1
.
s
s⎝
s⎠
s In this case, the helicopter rises 3.00 m during the 2.00 s interval while the mailbag
has a displacement of −18.1 m s + 1.50 m s ⎤
⎥ ( 2 .00 s ) = −16.6 m
2
⎣
⎦ ( ∆y )bag = ⎡
⎢ from the release point. Thus, the separation between the two at the end of 2 .00 s is
3.00 m − ( − 16.6 m ) = 19.6 m . 2.48 1
(a) Consider the relation ∆y = v i t + at 2 with a = − g . When the ball is at the throwers
2
1
hand, the displacement ∆y is zero, or 0 = v i t − gt 2 . This equation has two
2
solutions, t = 0 which corresponds to when the ball was thrown, and t = 2v i g
corresponding to when the ball is caught. Therefore, if the ball is caught at
t = 2 .00 s , the initial velocity must have been ( ) 9.80 m s 2 ( 2 .00 s )
gt
vi = =
= 9.80 m s .
2
2
(b) From v 2 = v i2 + 2 a( ∆y ) , with v f = 0 at the maximum height,
f ( ∆y )max = v 2 − v i2
f
2a = 0 − ( 9.80 m s ) ( 2 2 − 9.80 m s 2 ) = 4.90 m . 37 CHAPTER 2.49 2 (a) When it reaches a height of 150 m, the speed of the rocket is
v f = v i2 + 2a( ∆y ) = ( 50.0 ( ) m s ) + 2 2 .00 m s 2 (150 m ) = 55.7 m s .
2 After the engines stop, the rocket continues moving upward with an initial velocity
of v i = 55.7 m s and acceleration a = − g = −9.80 m s 2 . When the rocket reaches
maximum height, v f = 0 . The displacement of the rocket above the point where the
engines stopped (i.e., above the 150 m level) is ∆y = v 2 − v i2
f
2a = 0 − ( 55.7 m s ) ( 2 − 9.80 m s 2 2 ) = 158...
View
Full
Document
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

Click to edit the document details