A pitcher throws a 0.15-kg baseball so that it crosses
home plate horizontally with a speed of 20 m/s. The ball
is hit straight back at the pitcher with a final speed of
22 m/s. What is the impulse delivered to the ball?
A.
B.
C.
D.
r
r
I = ∆p
0.30 kg m/s
towards pitcher
0.30 kg m/s
toward batter I = Pf – Pi
6.3 kg m/s
= m(Vf-Vi)
toward pitcher
= 0.15 (-22 – 20) kg m/s
6.3 kg m/s
toward batter = -6.3 kg m/s
Negative means toward pitcher
Find the average force exerted by the bat
on the ball if the two are in contact for
From last page: impulse delivered
2.0 × 10–3 s.
to the ball = - 6.3 kg m/s
A.
B.
C.
D.
3.1 × 103 N
towards pitcher
3.1 × 103 N
towards batter
6.3 N towards
batter
6.3 N towards
pitcher
I = F ∆t
F = I/ ∆t
= -6.3/0.002 N
Quiz (will count for credit)
Mary Jane falls from a tower. Spiderman tries to
save her by catching her with his webbing. By
the time that the webbing reaches Mary Jane,
she is falling at 40 m/s. If the mass of Mary Jane
is 50 kg and the webbing stops her motion in 0.5
second, what is the net force on her during this
interval?
A. 500 N
B. 4000 N
C. 400 N
D. 500 N
E. 2000 N
r
r ∆p
F=
∆t
= 50*(0-(-40))/0.5 = 4000 N
Two objects collide head on. Their masses and
initial velocities are given. If the 10 kg mass has
a final velocity of -0.1 m/s, what is the final
velocity of the 1 kg mass?
1 m/s
-1 m/s
10 kg
A.
B.
C.
D.
-10 m/s
-1 m/s
0.1 m/s
10 m/s
1 kg
-0.1 m/s
? m/s
10 kg
1 kg
m1v1i + m2v2i = m1v1f + m2v2f
10 (1) + 1 (-1) = 10 (-0.1) +1 v2f