Module 3: Chapter 7 - Laws of Motion and Momentum

Question 1

What is momentum?

Answer 1

Momentum is a measure of how difficult it is to stop a moving object.
Momentum = mass x velocity

ρ = mv

Question 2

What are the units for momentum?

Answer 2

kgms⁻¹ / Ns

Question 3

What is newtons first law of motion?

Answer 3

An object at rest will stay at rest and an object in motion will remain in motion unless acted upon by an unbalanced force

Question 4

What is newtons second law of motion?

Answer 4

The rate of change of momentum of an object is directly proportional to the resultant force acting on the object
F = (mv - mu) / t

When m is constant them F = ma

Question 5

A tennis ball of mass 250g strikes a surface with a velocity of 15ms⁻¹. It rebounds directly backwards with a velocity of 7ms⁻¹. What is the change in momentum?

Answer 5

5.5kgms⁻¹

Question 6

What is the principle of conservation of linear momentum?

Answer 6

The total linear momentum of a system of interacting bodies is constant, providing no external forces act.

Question 7

What is a collision?

Answer 7

When objects move together and hit one another

Question 8

What is an explosion?

Answer 8

Where objects fly apart from one another after initially being at rest

Question 9

What is a perfectly elastic collision?

Answer 9

A collision in which the objects move in opposite directions after the collision.
* Momentum is conserved
* Total energy is conserved
* Kinetic energy is conserved

Question 10

What is an inelastic collision?

Answer 10

A collision in which objects stick together after the collision or move in the same direction
* Momentum is conserved
* total energy is conserved
* Kinetic energy is not conserved

Question 11

What is the equation for kinetic energy in terms of momentum?

Answer 11

Question 12

What is the equation for impulse?

Answer 12

Ft = mv - mu
I = mv - mu

Question 13

What is impulse?

Answer 13

The product of the force and the time the force acts, this is equal to the change in momentum

Question 14

What is the area under a force-time graph?

Answer 14

Impulse

Question 15

What is the equation for impulse from a force-time graph?

Answer 15

Question 16

What is the equation for impact force?

Answer 16

Impact Force = (mv - mu) / t

Question 17

How do safety features help keep passengers safe in the event of a car crash?

Answer 17

In a car crash, safety features help to increase the amount of time over which a collision occurs. This reduces the rate of change of momentum and therefore reduces the impact force experienced. Features include:
* Seatbelts - stretch slightly to prolong the passengers impact time
* Crumple zones - increase collision time
* Airbags - increase collision time and spread force across entire body

Question 18

A stationary radioactive nucleus of mass M ejects an α particle of mass m at a speed of 2x10⁷ ms⁻¹. Given M = 55m, calculate the kinetic energy of the α particle as a percentage of the final total kinetic energy

Answer 18

98.2%

Question 19

How do you solve a momentum collision question when the 2 particles move off at an angle to each other?

Answer 19

1. Resolve the inital momentum into vertical and horizontal components
2. The total vertical and total horizontal components must stay constant before and after the collision
3. Use final vertical and horizontal components to find the final momentum

Question 20

What is newtons third law of motion?

Answer 20

When 2 objects interact, they exert equal and opposite forces on each other

Question 21

What are the 4 fundamental forces?

Answer 21

• Gravitational
• Electrostatic
• Strong Nuclear
• Weak Nuclear

Question 22

Explain the interaction between pushing 2 objects together in terms of the 4 fundamental forces.

Answer 22

WHen you push 2 objects together, the contact you feel is due to the electrostatic repulsive forces between the electron clouds around the atomic nuclei in your hands.