7/25/2019 Momentum Conservation Problems

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245QUESTIONS

Questions

1 Figure 9-23 shows an overheadview of three particles on which ex-ternal forces act.The magnitudes anddirections of the forces on two of theparticles are indicated. What are themagnitude and direction of the forceacting on the third particle if the cen-ter of mass of the three-particle sys-tem is (a) stationary, (b) moving at aconstant velocity rightward,and (c) accelerating rightward?

2 Figure 9-24 shows an over-head view of four particles ofequal mass sliding over a fric-tionless surface at constantvelocity. The directions of thevelocities are indicated; theirmagnitudes are equal. Considerpairing the particles. Which

pairs form a system with a cen-ter of mass that (a) is stationary,(b) is stationary and at the ori-gin,and (c) passes through the origin?

3 Consider a box that explodes into two pieces while moving witha constant positive velocity along an x axis. If one piece, with massm1, ends up with positive velocity , then the second piece, withmass m2, could end up with (a) a positive velocity (Fig.9-25a), (b)a negative velocity (Fig. 9-25b), or (c) zero velocity (Fig. 9-25c).Rank those three possible results for the second piece according tothe corresponding magnitude of , greatest first.v1

:

v2:

v2:

v1:

boxes move over a frictionless confectioners counter.For each box,is its linear momentum conserved along thex axis and they axis?

6 Figure 9-28 shows four groups of three or four identical particles

that move parallel to either thex axis or they axis,at identical speeds.Rank the groups according to center-of-mass speed, greatest first.

y

15 N

3 N2

3

x

Figure 9-23 Question 1.

c d

a

y(m)

2

2 2 44

2

x(m)

b

Figure 9-24 Question 2.

v2 v2v1 v1

(b) (c)(a)

v1

Figure 9-25 Question 3.

2F0

4F0

6t0t

F F

t t

F

(a) (b) (c)

3t0 12t0

2F0

Figure 9-26 Question 4.

xxx

y y y

60

60

60608 6

5

4

6

8 3

4

2

2

6 5 2 3

(a) (b) (c)

Figure 9-27 Question 5.

4 Figure 9-26 shows graphs of force magnitude versus time for abody involved in a collision. Rank the graphs according to themagnitude of the impulse on the body, greatest first.

5

The free-body diagrams in Fig. 9-27 give, from overhead views,the horizontal forces acting on three boxes of chocolates as the

y

x

(a)

y

x

(c)

y

x

(b)

y

x

(d)

Figure 9-28 Question 6.

7 A block slides along a frictionless floor and into a stationary sec-ond block with the same mass. Figure 9-29 shows four choices for agraph of the kinetic energies Kof the blocks. (a) Determine whichrepresent physically impossible situations. Of the others, which bestrepresents (b) an elastic collision and (c) an inelastic collision?

K

t

(a)

K

t

(b)

K

t

(c)

K

t

(d)

Figure 9-29 Question 7.

8 Figure 9-30 shows a snapshot ofblock 1 as it slides along anx axis on africtionless floor, before it undergoesan elastic collision with stationaryblock 2.The figure also shows three possible positions of the center ofmass (com) of the two-block system at the time of the snapshot.(PointB is halfway between the centers of the two blocks.) Is block 1 station-ary, moving forward,or moving backward after the collision if the comis located in the snapshot at (a)A,(b) B,and (c)C?

1 2A B C

Figure 9-30 Question 8.