Question 1

A 50.0 g air-hockey disk moves west at 0.80 m/s and collides perfectly inelastically with three other disks: 60.0 g north at 2.50 m/s, 100.0 g east at 0.20 m/s, and 40.0 g south at 0.50 m/s. What is the magnitude of the final velocity of the combined disks after the collision?

Accepted Answer

$$0.52 \, \mathrm{m/s}$$

Question 2

In the previous problem, what is the direction (angle from the positive x-axis) of the final velocity of the combined disks?

Accepted Answer

$$98.7^\circ$$

Question 3

Which of the following best describes the type of collision in the air-hockey disk problem above?

Accepted Answer

Perfectly inelastic collision

Question 4

Becka (40.0 kg) skates at $$12.5 \, \mathrm{m/s}$$ and collides with stationary Danny (600 N). After the collision, Becka moves at $$10.0 \, \mathrm{m/s} at$$ $$37^\circ$$ from her original direction. What is the magnitude of Danny's final velocity?

Accepted Answer

$$5.01 \, \mathrm{m/s}$$

Question 5

What is the direction (angle from the positive x-axis) of Danny's final velocity after the collision with Becka?

Accepted Answer

$$53.1^\circ$$

Question 6

Which of the following statements is true about the collision between Becka and Danny?

Accepted Answer

The collision is inelastic because kinetic energy is not conserved.

Question 7

Which equation correctly expresses the conservation of momentum in two dimensions for the air-hockey disk collision?

Accepted Answer

$$m_1$$ \vec{v}_{1i} + $$m_2$$ \vec{v}_{2i} + $$m_3$$ \vec{v}_{3i} + $$m_4$$ \vec{v}_{4i} = ($$m_1$$ + $$m_2$$ + $$m_3$$ + $$m_4$$) \vec{v}_f$$

Question 8

If kinetic energy is not conserved in a collision, which of the following must be true?

Accepted Answer

The collision is inelastic.

Question 9

A 0.025 kg marble moving at $$0.50 \, \mathrm{m/s}$$ strikes a stationary 0.100 kg steel marble. If the cat’s eye marble stops, what is the velocity of the steel marble after the collision?

Accepted Answer

$$0.125 \, \mathrm{m/s}$$

Question 10

Which of the following best describes a perfectly inelastic collision?

Accepted Answer

The colliding objects stick together after the collision.

Question 11

A 1400 kg car moving north at $$45 \, \mathrm{km/h}$$ collides with a 2500 kg truck moving east at $$33 \, \mathrm{km/h}. $$What is the magnitude of the final velocity of the combined vehicles if they stick together?

Accepted Answer

$$7.40 \, \mathrm{m/s}$$

Question 12

Which of the following is always conserved in any collision (elastic or inelastic) if no external forces act?

Accepted Answer

Momentum

Momentum and Conservation of Momentum: Collisions and Explosions

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