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Review of Linear Momentum
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1. The center of mass is defined as
The position of the most massive particle in a given system
The point at which a net external force applied to all the mass of the system at that point would produce the same acceleration of the system as if it were applied to each particle individually
The average position of each particle
The point equidistant from all particles in a system
2. The equation for the center of mass of two particles is
x
_{cm}
=
x
_{cm}
=
m
_{1}
x
_{1}
+
m
_{2}
x
_{2}
x
_{cm}
=
x
_{cm}
=
3. A particle of mass 1 kg is located at (0,0) and a particle of mass 2 kg is located at (3,0). What is the location of the center of mass of this system?
(0,0)
(1,0)
(1.5,0)
(2,0)
4. The net external force on a system of particles is zero. What is the velocity of the center of mass of the system?
0
Constant
Constantly increasing
Constantly decreasing
5. The net external force on a system of particles is zero. What is the velocity of each particle in the system?
0
Constant
Constantly increasing
Not enough information
6. Four particles of equal mass are at points (0,0), (2,0), (2,2) and (0,2). Where is the center of mass of the system?
(1,0)
(1,1)
(2,0)
(2,2)
7. Where is the center of mass of a single particle?
The point halfway between the particle and the origin
The origin
The position of the particle
Undefined
8. A net force of 8 N is applied to a system containing four masses, each of 1kg. What is the resultant acceleration of the center of mass of the system?
2 m/s
8 m/s
12 m/s
32 m/s
9. What is the definition of impulse?
Force per unit time
Force per unit distance
Force over a distance
Force over a time
10. What is the equation for impulse?
F/t
Ft
Fx
11. A bat exerts a force on a ball of 100 N for a period of .1 seconds. What is the impulse provided by the bat?
100
10
1000
10
12. What is the definition of momentum?
ma
mv
^{2}
mv
^{2}
mv
13. A net impulse on an object causes
A change in its kinetic energy
A change in its speed
A change in its momentum
A change in its mass
14. What is the relation between force and momentum?
F
=
Δp
F
=
F
=
pt
F
=
px
15. A ball of mass 2 kg bounces against a wall with a velocity of 6 m/s and rebounds with the same velocity. What is the impulse provided by the wall?
12
24
3
8
16. What are the units of momentum, in terms of fundamental units?
N-s
kg-m/s
J/s
kg-m
17. What are the units of impulse, in terms of fundamental units?
N-s
kg-m/s
J/s
kg-m
18. Both momentum and kinetic energy are dependent on what variable?
Acceleration
Position
Work
Velocity
19. A 4 kg mass has a momentum of 2 N-s. What is the kinetic energy of the mass?
1 J
2 J
8 J
Cannot be determined
20. What is the mass of an object that moves 10 meters in 2 seconds, and has a momentum of 10 N-s?
1 kg
2 kg
5 kg
10 kg
21. What is the definition of the momentum of a system of particles?
P
=
M
(
v
_{1}
+
v
_{2}
+
^{ ... }
+
v
_{n}
)
P
=
Mv
_{1}
v
_{2}
^{ ... }
v
_{n}
P
=
Mv
_{cm}
P
=
Ma
_{cm}
22. The total momentum of a system of particles is conserved only if
There are no interactions between the particles
The velocity of the center of mass of the system is constant
The velocity of the center of mass of the system is zero
The system conserves energy
23. What is the linear momentum of a system of two particles with equal mass m travelling in opposite directions with speed v?
0
2mv
mv
mv/2
24. A cannon of mass 100 kg fires a shell of mass 10 kg at a speed of 100 m/s. With what speed does the cannon recoil?
0
1 m/s
100 m/s
10 m/s
25. A missile explodes in midair. What statement can be made about the motion of the system after the explosion?
Each fragment from the explosion falls directly to the ground.
The center of mass of the system continues in the same path as the missile before the explosion.
The center of mass of the system moves with constant velocity.
The total linear momentum of each piece of the explosion is zero.
26. A mass of 2 kg moves in the positive x direction with a speed of 2 m/s. A mass of 1 kg moves in the negative x direction with a speed of 3 m/s. What is the total momentum of this system?
1 kg-m/s
7 kg-m/s
8 kg-m/s
5 kg-m/s
27. A mass of 2 kg moves in the positive x direction with a speed of 2 m/s. A mass of 1 kg moves in the negative x direction with a speed of 3 m/s. What is the velocity of the center of mass of this system?
1 m/s
2 m/s
.33 m/s
.66 m/s
28. If the total linear momentum of a system is zero, it can be deduced that
The center of mass of the system has no velocity
No particles in the system are moving
No net external force is acting upon the system
There are no forces between particles in the system
29. In which of the following situations is momentum NOT conserved?
Two objects colliding
A group of skydivers falling to the earth
An object moving horizontally with constant speed
A rocket in deep space firing its engines
30. Two cars of equal mass collide head on and both come to a stop. What can be said about the cars before the crash?
The velocity of each car was relatively low
They were moving in the same direction
They put on their brakes
They were moving with equal speeds in opposite directions
31. A baseball of mass 1 kg is hit by a bat, changing its velocity from 50 m/s in one direction to 50 m/s in the opposite direction. What is the impulse provided by the bat?
100 N-m
50 N-m
25 N-m
10 N-m
32. A baseball of mass 1 kg is hit by a bat, changing its velocity from 50 m/s in one direction to 50 m/s in the opposite direction. The bat is in contact with the ball for .1 seconds. What is the average force provided by the bat over this time?
100 N
50 N
500 N
1000 N
33. A net force of 50 N acts on a particle for 1 second. What is the impulse provided by the force?
100 N-s
25 N-s
50 N-s
150 N-s
34. A net force of 50 N acts on a particle of mass 5 kg for 1 second. What is the change in the velocity of the particle?
50 m/s
25 m/s
5 m/s
10 m/s
35. Are impulse and momentum vector or scalar quantities?
Impulse is a vector, momentum is a scalar
Impulse is a scalar, momentum is a vector
Both are vectors
Both are scalars
36. What is the definition of an elastic collision?
Momentum is conserved
The velocity of the center of mass of the system does not change
Kinetic energy is conserved
Both particles retain their original velocities
37. What is the definition of a completely inelastic collision?
The two particles stick together
Momentum is not conserved
Kinetic energy is not conserved
Both particles have a final velocity of zero
38. Two particles of the same mass and speed collide head on in an elastic collision. What can be said about the final velocity of each particle?
They are both zero
They are both the same as their initial velocities
The have the same magnitude and opposite direction as their initial velocities
Not enough information
39. Which of the following problems, given initial conditions of mass and velocity of each particle, is NOT solvable?
A head on elastic collision
A two dimensional elastic collision
A head on completely inelastic collision
A two dimensional completely inelastic collision
40. A particle of mass 1 kg moving at a velocity of 50 m/s hits a particle of mass 1 kg, at rest in an elastic collision. What is the final velocity of the second particle?
0
25 m/s
100 m/s
50 m/s
41. A particle of mass 1 kg moving at a velocity of 50 m/s hits a particle of mass 1 kg, at rest in a completely inelastic collision. What is the final velocity of the second particle?
0
25 m/s
100 m/s
50 m/s
42. A particle of mass 1 kg moving along the x axis collides with a particle of mass 1 kg moving along the y axis with the same speed in a completely inelastic collision. What is the angle each particle makes with the x axis?
45
^{o}
90
^{o}
180
^{o}
0
^{o}
43. How many equations can we use to solve a one dimensional elastic collision problem?
1
2
3
4
44. How many equations can we use to solve a one dimensional completely inelastic collision problem?
1
2
3
4
45. How many equations can we use to solve a two dimensional elastic collision problem?
1
2
3
4
46. How many equations can we use to solve a two dimensional completely inelastic collision problem?
1
2
3
4
47. In EVERY collision problem, what is conserved?
Kinetic energy
Total mechanical energy
The sum of the velocities of the particles involved
Momentum
48. A particle at rest explodes into two pieces. What can be said about the motion of each piece?
They both are stationary after the explosion
They must move in opposite directions
They must have equal masses
Nothing can be said without knowing the nature of the explosion
49. The collision of two pool balls is approximately what kind of collision?
Inelastic
Elastic
Completely inelastic
Depends on the nature of the collision
50. In any isolated system (with no external forces acting) which of the following is NOT conserved?
Momentum
Energy
Kinetic energy
The velocity of the center of mass of the system
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