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U N I V E R S I T Y
OF
W I N D S O R
DEPARTMENT OF PHYSICS
Physics 64140
Assignment No. 10
Name:
Assigned:
Wednesday, November 25
th
, 2009
I.D.#:
Due: MONDAY, November 30
th
, 2009
1). Page 233 36
The figure shows an overhead view of a 300 g ball with a
speed
v
of 6.0 ms
1
strikes a wall at an angle
θ
of 30º and
then rebounds with the same speed and angle. It is contact
with the wall for 10 ms. In unit vector notation, what are (a)
the impulse on the ball from the wall and (b) the average
force on the wall from the ball?
In the figure +
y
corresponds to the direction of the rebound (directly away from the wall) and +
x
towards the right. Using unitvector notation, the ball’s initial and final velocities are:
ˆˆ
ˆ
cos i
sin
j 5.2 i 3.0 j
ˆ
cos
i
sin
j 5.2 i
3.0 j
i
f
vv
v
v
θθ
=−=
−
=+
=
+
G
G
ˆ
ˆ
respectively (with SI units understood).
(a) With
m
= 0.30 kg, the impulsemomentum theorem yields
( )
2 0.30 kg (3.0 m/s j)
(1.8 N s)j
fi
Jm
v m
v
=−
=
=
⋅
G
GG
(b) The force on the ball by the wall is
ˆ
(1.8 0.010)j
(180 N) j.
Jt
Δ=
=
G
ˆ
By Newton’s third law,
the force on the wall by the ball is
(that is, its magnitude is 180 N and its direction is
directly into the wall, or
“down”
in the view given in the figure).
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 Spring '10
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