Question 1

A 1000 kg car is traveling north at 15 m/s and collides at an intersection with a 2000 kg truck traveling east at 10 m/s. What is the magnitude of the total momentum of the system just before the collision?

Accepted Answer

$$18028\ \mathrm{kg\cdot m/s}$$

Question 2

Which of the following best describes a perfectly inelastic collision?

Accepted Answer

The objects stick together and move as one mass after the collision.

Question 3

A rifle of mass $$3.00\ \mathrm{kg}$$ fires a $$5.00\ \mathrm{g}$$ bullet at $$300\ \mathrm{m/s}. $$What is the recoil velocity of the rifle?

Accepted Answer

$$-0.50\ \mathrm{m/s}$$

Question 4

Which of the following statements about momentum is correct?

Accepted Answer

Momentum is a vector and must be considered in each direction separately.

Question 5

A $$0.300\ \mathrm{kg}$$ glider moving at $$0.80\ \mathrm{m/s}$$ collides elastically with a stationary $$0.150\ \mathrm{kg}$$ glider. What is the velocity of the $$0.150\ \mathrm{kg}$$ glider after the collision?

Accepted Answer

$$0.53\ \mathrm{m/s}$$

Question 6

Which equation correctly expresses the impulse delivered to an object by a constant force $$\vec{F}$$ over a time $$\Delta t$$?

Accepted Answer

$$\vec{J} = \vec{F}_{\mathrm{avg}} \Delta t$$

Question 7

A $$0.40\ \mathrm{kg}$$ ball moving at $$-30\ \mathrm{m/s}$$ bounces off a wall and rebounds at $$20\ \mathrm{m/s}. $$What is the impulse delivered to the ball by the wall?

Accepted Answer

$$20\ \mathrm{kg\cdot m/s}$$

Question 8

In a ballistic pendulum experiment, a $$2.6\ \mathrm{g}$$ bullet is fired into a $$0.5\ \mathrm{kg}$$ block, and the block rises to a height of $$17\ \mathrm{cm}. $$What is the initial speed of the bullet? (Assume perfectly inelastic collision and conservation of energy after collision.)

Accepted Answer

$$380\ \mathrm{m/s}$$

Question 9

Which of the following is true about the center of mass of a system?

Accepted Answer

It is the point where the total mass of the system can be considered to be concentrated for translational motion.

Question 10

A $$8.5\ \mathrm{g}$$ bullet is fired at $$900\ \mathrm{m/s}. $$What is the impulse imparted to the bullet?

Accepted Answer

$$7.65\ \mathrm{kg\cdot m/s}$$

Question 11

Which of the following best describes an elastic collision?

Accepted Answer

Total kinetic energy and total momentum are both conserved.

Question 12

A shell explodes in midair. What happens to the center of mass of the system after the explosion?

Accepted Answer

It follows the original trajectory as if the explosion had not occurred.

Question 13

Which formula gives the $$x-$$coordinate of the center of mass for a system of particles?

Accepted Answer

$$x_{cm} = \frac{m_A x_A + m_B x_B + m_C x_C + \cdots}{m_A + m_B + m_C + \cdots}$$

Question 14

A force acts on an object for a longer duration but with a lower peak value compared to a short, high peak force. If both deliver the same impulse, what can be said about the change in momentum?

Accepted Answer

The change in momentum is the same for both cases.

Question 15

In a two-dimensional collision, why must momentum be conserved in both the $$x$$ and $$y$$ directions?

Accepted Answer

Because momentum is a vector and each component must be conserved independently.

Question 16

A $$0.300\ \mathrm{kg}$$ glider moving at $$0.80\ \mathrm{m/s}$$ collides elastically with a stationary $$0.150\ \mathrm{kg}$$ glider. What is the velocity of the $$0.300\ \mathrm{kg}$$ glider after the collision?

Accepted Answer

$$0.27\ \mathrm{m/s}$$

Question 17

Which of the following is the correct vector equation for the total momentum of a system of particles?

Accepted Answer

$$\vec{P} = \vec{p}_1 + \vec{p}_2 + \cdots$$

Question 18

A dancer leaps into the air. What path does her center of mass follow?

Accepted Answer

A parabolic trajectory determined by her initial velocity and gravity.

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