Chapter 8: Linear Momentum and Collisions

Question 1

Define change in momentum

Answer 1

the difference between the final and initial momentum; the mass times the change in velocity

Question 2

Define conservation of momentum principle

Answer 2

when the net external force is zero, the total momentum of the system is conserved or constant

Question 3

Define elastic collisions

Answer 3

a collision that also conserves internal kinetic energy

Question 4

Define impulse

Answer 4

the average net external force times the time it acts; equal to the change in momentum

Question 5

Define inelastic collision

Answer 5

a collision in which internal kinetic energy is not conserved

Question 6

Define internal kinetic energy

Answer 6

the sum of the kinetic energies of the objects in a system

Question 7

Define isolated system

Answer 7

a system in which the net external force is zero

Question 8

Define linear momentum

Answer 8

the product of mass and velocity

Question 9

Define perfectly inelastic collision.

Answer 9

a collision in which the colliding objects stick together

Question 10

Define point masses:

Answer 10

structureless particles with no rotation or spin

Question 11

Define quark

Answer 11

fundamental constituent of matter and an elementary particle

Question 12

Define second law of motion

Answer 12

physical law that states that the net external force equals the change in momentum of a system divided by the time over which it changes

Question 13

What is the equation for linear momentum

Answer 13

p=mv

p=momentum
m=mass
v=velocity

Question 14

What is the unit for momentum?

Answer 14

kgm/s

Question 15

What is Newton’s second law in symbols?

Answer 15

Fnet = ΔpΔt

Question 16

What is the equation for impulse?

Answer 16

Δp = fnet Δt

Question 17

How to calculate acceleration

Answer 17

a = ΔV / ΔT

ΔV = V-Vo

Question 18

What are the two type of collisions?

Answer 18

Elastic and inelastic

Question 19

What is elastic collions?

Answer 19

Where kinetic energy is conserved

Question 20

What is inelastic collision?

Answer 20

Kinetic energy is lost in the collision.

Question 21

Elastic collisions mostly occur…

Answer 21

In microscopic particles

Question 22

How to calculate the veloctiy of the center of mass?

Answer 22

Vcom = (m1v1+m2v2)/m1+m2

Question 23

A person slaps her leg with her hand, which results in her hand coming to rest in a time interval of 2.65 ms from an initial speed of 3.25m/s. What is the magnitude of the average contact force exerted on the leg, assuming the total mass of the hand and the forearm to be 1.65kg?

Answer 23

2023.6 N

Explanation:

I. Assess what you have: time interval, initial speed, and mass

II. Assess what you need: average force

III: Find a fitting equation: Δ𝑝=𝐹Δ𝑡
a. Rearrange equation –> F = Δ𝑝/Δ𝑡
b. substitute with what we have –> F = m(vf-vi)/Δ𝑡
c. Since final velocity is 0 we get our final equation…
d. F = -mvi / Δ𝑡

IV. Plug in numbers: F = -(1.65kg)(3.25m/s) / 2.65x10^-3

V. Solve: 2023.6

Question 24

Calculate the momentum Pelephant of a 2060kg elephant charging a hunter at a speed of 7.51m/s

Answer 24

p = mv

p = 2060 kg * 7.51m/s

p = 15,470.6 kgm/s

Question 25

What is the momentum Phunter of the 87.0kg hunter running at 7.39m/s after missing the elephant?

Answer 25

642.93kgm/s

p = mv

p = 87 * 7.39

p = 642.93

Question 26

A large semitailer truck and a small car have equal momentum. How do their speeds compare?

Answer 26

The truck has a much slower speed than the car.

Explanation:
If the masses are only slightly different, then the speeds will be only slightly different. In this case, there is a large semitrailer truck and a small car.

Question 27

A rubber ball and a wet lump of clay, both with mass 6kg, are thrown at a wall with the same speed, 6m/s. The ball bounces off the wall with no loss of speed, but the clay sticks.

What is the change in momentum of the clay and the ball, respectively?

Answer 27

Ball: -36 kgm/s
Clay: -72kgm/s

The inital momentum of them is the same. p=mv –> p = 6kg * 6m/s = 36kgm/s

Since the ball bounces off but keeps going it is just the opposite direction, -36kgm/s. But since the clay stops it doubles to -72kgm/s