w
=
mg
= (0.200 kg)(9.80 m/s
2
) = 1.96 N.
So the total force is
22.0 N + 1.96 N = 24.0 N upward
.
26.
(a) Hitting it back
requires a greater force.
Force is proportional to the change in momentum.
When a
ball changes its direction, the change in momentum is greater. If
∆
p
=
p
1
−
p
2
and
p
1
and
p
2
are
opposite (hitting it back), then
∆
p
=
p
1
– (
−
p
2
) =
p
1
+
p
2
.
Had you caught the ball, then
p
2
= 0 so
∆
p
=
p
1
.
(b) The final velocity is opposite to the initial velocity (“hitting it back”).
F
avg
=
∆
p
∆
t
=
mv
−
mv
o
∆
t
=
(0.45 kg)(
−
7.0 m/s
−
4.0 m/s)
0.040 s
=
−
1.2
×
10
2
N =
1.2
×
10
2
N in direction opposite
v
o
.

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