7.1
On August 10, 1972, a large meteorite skipped across the atmosphere above
the western United States and western Canada, much like a stone skipped across
water. The accompanying fireball was so bright that it could be seen in the daytime
sky and was brighter than the usual meteorite trail. The meteorite’s mass was about
4x10
6
kg
; its speed was about 15 km/s. Had it entered the atmosphere vertically,
it would have hit Earth’s surface with about the same speed. (a) Calculate the
meteorite’s loss of kinetic energy (in joules) that would have been associated with
the vertical impact. (b) Express the energy as a multiple of the explosive energy of
1 megaton of TNT, which is 4.2x10
15
J. (c) The energy associated with the atomic
bomb explosion over Hiroshima was equivalent to 13 kilotons of TNT. To how
many Hiroshima bombs would the meteorite impact have been equivalent?
2
6
2
14
f
i
1
1
m
K
K
K
0J
mv
(4.0x10 kg)(15000
)
4.5x10
J
2
2
s
Δ
=
−
=
−
= −
= −
a)
b)
14
15
1megaton TNT
K
( 4.5x10
J)
0.107 megaton TNT
4.2x10
J
Δ
= −
= −
c)
1Hiroshima bomb
0.107megaton TNT
107 kiloton TNT
8.24 Hiroshima bomb
13 kiloton TNT
⎛
⎞
=
=
⎜
⎟
⎝
⎠
(the problem asks for the energy as
a multiple
of the explosive energy which
is really a dimensionless quantity)
(negative sign expresses loss
of kinetic energy)

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