http://www.ck12.org Chapter 7. Momentum
FIGURE 7.8
Impulse experienced by ball. The graph on the right shows that the force on the baseball is not constant.(b) What is the magnitude of the average force the ball experiences?
Recall the mass of the ball is 0.145-kg and the velocity is 46.95 m/s.
Answers:
a. In an earlier example, we showed that the change in momentum∆pwas:
∆p=pf−pi=− 6. 808 −(+ 6. 808 ) =− 13. 62 →− 13. 6 kg∗smor a magnitude of 13. 6 kg∗sm
(Note-the negative sign indicates that the direction of the force on the ball is opposite to the ball’s incoming
direction.)
Since∆p=F∆t,the impulse the ball experiences is -13.6 N-s
b. The magnitude of the average force isF ̄=∆∆pt= 013. 70.^6 ×N 10 −−s 3 = 19428 = 1. 9 × 104 N
Illustrative Example 7.2.2
We continue with our baseball example with a question for the catcher. It is a very good idea when catching a fastball
to move your arm back as you catch the ball. Let’s determine the force on the catcher’s mitt under two conditions:
(1) The catcher moves his arm back 1.00-cm in catching the ball and
(2) The catcher moves his arm back 10.00-cm in catching the ball.
We use the values given in the original problem:m= 0. 145 −kgandvi= 46. 95 ms, in addition to the two displacements-
1.00-cm and 10.00-cm- to solve the problem.