Q: A 0.0200 kg bullet traveling at 794 m/s embeds itself in a 5.7500 kg pendulum. After the collision, the combined mass swings upward to a height of 0.386 m. What is the velocity of the pendulum-bullet system immediately after the collision?

$$v = \sqrt{2 \times 9.81 \times 0.386} = 2.75\ \text{m/s}$$

Q: Which equation is used to determine if a collision is elastic or inelastic?

$$E_{k,\text{initial}} = E_{k,\text{final}}$$

Q: A 1.20 kg ball moving at 17.1 m/s collides with a stationary 2.31 kg ball. After the collision, the first ball moves at 13.5 m/s and the second at 3.66 m/s. What is the total kinetic energy after the collision?

$$E_k = \frac{1}{2} \times 1.20 \times (13.5)^2$ + \frac{1}{2} \times 2.31 \times (3.66)^2$ = 125\ \text{J}$$

Q: In the ballistic pendulum example, what percentage of the bullet's initial kinetic energy remains after the collision?

$$\frac{21.8}{6304.36} \times 100 \approx 0.346\%$$

Question 1

Which of the following statements best describes an elastic collision?

Accepted Answer

Total kinetic energy before and after the collision is the same, and momentum is conserved.

Question 2

A 2.0 kg object moving at 5.0 m/s collides elastically with a stationary 3.0 kg object. After the collision, the 2.0 kg object moves at 2.0 m/s. What is the velocity of the 3.0 kg object after the collision?

Accepted Answer

Question 3

Which of the following is NOT a way kinetic energy can be 'lost' in an inelastic collision?

Accepted Answer

Conversion to gravitational potential energy during the collision

Question 4

In a completely inelastic collision, what happens to the colliding objects?

Accepted Answer

They stick together and move as a single mass after the collision.

Question 5

A 0.0200 kg bullet traveling at 794 m/s embeds itself in a 5.7500 kg pendulum. After the collision, the combined mass swings upward to a height of 0.386 m. What is the velocity of the pendulum-bullet system immediately after the collision?

Accepted Answer

$$v = \sqrt{2 	imes 9.81 	imes 0.386} = 2.75\ 	ext{m/s}$$

Question 6

Which equation is used to determine if a collision is elastic or inelastic?

Accepted Answer

$$E_{k,	ext{initial}} = E_{k,	ext{final}}$$

Question 7

A collision between two pool balls is most likely:

Accepted Answer

Elastic, with almost all kinetic energy conserved

Question 8

In the ballistic pendulum experiment, why is conservation of momentum used to find the bullet's speed before impact, rather than conservation of energy?

Accepted Answer

Because momentum is conserved during the collision, but kinetic energy is not

Question 9

If two objects collide and stick together, which type of collision has occurred?

Accepted Answer

Completely inelastic

Question 10

A 1.20 kg ball moving at 17.1 m/s collides with a stationary 2.31 kg ball. After the collision, the first ball moves at 13.5 m/s and the second at 3.66 m/s. What is the total kinetic energy after the collision?

Accepted Answer

$$E_k = \frac{1}{2} 	imes 1.20 	imes (13.5)^2$ + \frac{1}{2} 	imes 2.31 	imes (3.66)^2$ = 125\ 	ext{J}$$

Question 11

Which of the following is true for all collisions, regardless of whether they are elastic or inelastic?

Accepted Answer

Momentum is always conserved.

Question 12

A collision between two atoms is most likely:

Accepted Answer

Elastic, with kinetic energy conserved

Question 13

Which formula is used to calculate the kinetic energy of an object?

Accepted Answer

$$E_k = \frac{1}{2} m v^2$

Question 14

After a collision, the total kinetic energy is found to be less than before. What type of collision has occurred?

Accepted Answer

Inelastic

Question 15

In the ballistic pendulum example, what percentage of the bullet's initial kinetic energy remains after the collision?

Accepted Answer

$$\frac{21.8}{6304.36} 	imes 100 \approx 0.346\%$$

Question 16

Which of the following is NOT a characteristic of an elastic collision?

Accepted Answer

Objects stick together after the collision

Question 17

Why are collisions between macroscopic objects, like cars or watermelons, usually inelastic?

Accepted Answer

Because some kinetic energy is converted to heat, sound, or deformation

Question 18

Which calculation would you use to determine the speed of a bullet in a ballistic pendulum experiment?

Accepted Answer

$$m_b v_b = v' (m_p + m_b) \Rightarrow v_b = \frac{v' (m_p + m_b)}{m_b}$$

Question 19

Which of the following statements is true regarding the use of angles in collision calculations for elastic and inelastic collisions?

Accepted Answer

Angles are not needed because kinetic energy is a scalar quantity.

Elastic and Inelastic Collisions: Physics Study Notes

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