(5) Forces and Motion

Question 1

Define distance:

Answer 1

Distance is how far an object moves, it doesn’t involve direction (scalar quantity)

Question 2

Define displacement:

Answer 2

Displacement includes both the distance an object moves (measured in a straight line from start to finish) and the direction. (Vector quantity)

Question 3

What are the typical values for the speeds of: sound, human walking, running and cycling

Answer 3

Sound = 330 m/s
Human walking = 1.5 m/s
Human running = 3 m/s
Cycling = 6 m/s

Question 4

What factors does the speed of walking, running or cycling depend on?

Answer 4

• age
• terrain
• fitness
• distance travelled

Question 5

What is the equation linking distance speed and time?

Answer 5

Distance = speed x time

Question 6

Why can an object travelling at a constant speed in a circle not have a constant velocity?

Answer 6

• speed is a scalar quantity
• velocity is a vector meaning is can only be constant if the direction is constant and in a circular motion the direction is continuously changing

Question 7

How can speed be calculated from a distance time graph?

Answer 7

Speed is equal to the gradient of the graph

Question 8

How do you calculate speed from a distance time graph for an accelerating object?

Answer 8

Draw a tangent to the curve at the required time and calculate the gradient

Question 9

What is the equation for acceleration?

Answer 9

Acceleration = change is velocity / time taken

Question 10

How can the distance travelled by an object be calculated from a velocity time graph?

Answer 10

Equal to the area under the graph

Question 11

What is the equation for velocity?

Answer 11

(Final velocity)² - (initial velocity)² = 2 x acceleration x distance

[ v² - u² = 2 x a x s ]

Question 12

What is an approximate value for the acceleration of an object in free fall under the earths surface?

Answer 12

9.8 m/s

Question 13

What can be said about the resultant force acting on an object when it is falling at terminal velocity?

Answer 13

It’s is zero

• when at terminal velocity the object is moving at a constant speed and so isn’t accelerating

Question 14

State Newton’s first law for stationary objects:

Answer 14

If the resultant force on a stationary object is zero, the object will remain at rest

Question 15

State Newton first law for a moving object?

Answer 15

If the resultant force on a moving object is zero, the object will remain at a constant velocity (same speed in the same direction)

Question 16

What happens to the resultant force is an object is going at a constant speed?

Answer 16

If an object is at a constant speed, the resultant forces is balanced with driving force and the velocity of an object only changes if a resultant force is acting on it.

Question 17

What is inertia?

Answer 17

The tendency to resist any change in motion, staying at rest or uniform motion

Question 18

What is Newton’s second law?

Answer 18

The acceleration of an object is proportional to the resultant force acting on the object and inversely proportional to the mass of an object

Question 19

State the equation for Newton’s second law?

Answer 19

Resultant force = mass x acceleration

Question 20

What is inertial mass?

Answer 20

A measure of how difficult it is to change the velocity of an object. It is defined as the ratio of force over acceleration

Question 21

REQUIRED PRACTICAL 6: effect of force on acceleration on an object if constant mass

Answer 21

Measuring how long it takes for a trolly to move distance with diff et forces applied to it. Set up on a bench pulley with a meter ruler, string and weight stack.

Question 22

What is Newton’s third law?

Answer 22

Whenever two objects interact, the forces they exert on each other are equal and opposite. (Can be used in equilibrium situations)

Question 23

What is the stopping distance of a vehicle equal to?

Answer 23

Equal to the sum of the distance the vehicle travels during the driver reaction time (thinking distance) and the distance it travels under the braking force.

Question 24

For a given braking distance, if the vehicles speed is increased what happens to the braking distance?

Answer 24

The greater the speed of the vehicle the greater the stopping distance

Question 25

What are the typical reaction times of humans?

Answer 25

0.2s - 0.9s

Question 26

What factors affect the drivers reaction time?

Answer 26

• tiredness
• drugs
• alcohol

Question 27

What factors affect braking distance?

Answer 27

• Icy roads
• Wind
• Poor vehicle condition

Question 28

Describe the energy transfers that take place when a car applies it brakes:

Answer 28

Work done by the friction force between the brakes and the wheel reduces the kinetic energy of the vehicle (increasing the temperature of the brakes)

Question 29

Does a greater braking force cause larger or smaller deceleration?

Answer 29

Larger deceleration

These may cause brakes to overheat and the driver may also lose control of the vehicle.