Topic 1: Forces and Motion (PAPER ONE)

Question 1

What are the typical speeds for different transport methods?

Answer 1

Walking - 1.4 m/s
Running - 3 m/s
Cycling - 5.5 m/s
Cars (built up area) - 13 m/s
Aeroplanes - 250 m/s
Cars (on a motorway) - 31 m/s
Trains - 55 m/s
Wind speed - 5 to 20 m/s
Speed of sound in air - 340 m/s
Ferries - 15 m/s

Question 2

What’s are vectors and scalars?

Answer 2

Vector - a quantity that has direction and magnitude
Scalar - a quantity that has magnitude but no direction

Question 3

What’s acceleration?

Answer 3

The change in velocity in a certain amount of time

Question 4

How do you find the Speed on a distance/time graph, when it is a straight line?

Answer 4

Gradient = change in vertical/change in horizontal

Question 5

How do you find the average speed on a distance/time graph when the line is non-uniform (e.g. accelerating)?

Answer 5

Distance/time

Question 6

How do you find the speed on a distance/time graph if the line is curved?

Answer 6

Draw a tangent and find the gradient of it

Question 7

What’s a force?

Answer 7

A push/pull that acts on an object due to the interaction with another object (vector)

Question 8

What’s a contact force?

Answer 8

A force that acts when objects are physically touching

Question 9

What’s a non-contact force?

Answer 9

A force that acts when objects are not touching

Question 10

What are the three non-contact forces?

Answer 10

Gravitational force
Electromagnetic force
Magnetic force

Question 11

When do forces arise?

Answer 11

Forces arise from an interaction between two objects.
When two objects interact both experience a force.

Question 12

What is friction?

Answer 12

Friction is the interaction between two surfaces that slide relative to each other
Each surface experiences a force in the direction that prevents relative movement.

Question 13

What is normal contact force?

Answer 13

There is an interaction between an object and the surface it is resting on.
The object pushes down on the surface and the surface pushes up on the object with an equal force.

Question 14

What’s that resultant force?

Answer 14

The single force that could replace all forces acting upon an object

Question 15

How do you calculate the resultant force if it is not on a straight line?

Answer 15

(draw on graph paper, measure with a ruler the hypotenuse of the 2 forces) - triangle thingy: 1cm = 1 N

Question 16

What is newton’s second law?

Answer 16

The acceleration of an object is proportional to the resultant force of the object and inversely proportional to the mass of the object (f = ma)

Question 17

What is weight?

Answer 17

The force acting on an object due to gravity
weight = mass x gravitational field strength

Question 18

What apparatus can be used to measure weight?

Answer 18

Newton Meter

Question 19

What’s Newton’s third law?

Answer 19

When two objects interact, the forces they exert on each other are equal and opposite

Question 20

How can you investigate the effect of varying the force on the acceleration of an object?

Answer 20

CORE PRACTICAL:
- Measure the mass of a trolley and the hanging hook, and set up the trolley onto a ramp (measure the height)
- Set up two light gates, one at the start, one at the end
- As the trolley begins to move, the first light gate will record the initial speed
- Attach the trolley to the hanging mass by the string and let go
- Each light gate will record he time and the speed at that time
- Then calculate the acceleration using acceleration = change in speed/ time
- Repeat with more weight in even intervals

Question 21

Explain how safety features in vehicles work

Answer 21

• Increase collision time which reduces the force and risk of injury
• e.g. crumple zones increase time taken to stop which decreases its deceleration, reducing the force
• Air bags slow you down gradually

Question 22

How do vehicles skid?

Answer 22

• Brakes of a vehicle do work on its wheels which transfers energy from the vehicle’s kinetic energy store to the thermal energy store of the brakes
• Large decelerations may cause the brakes to overheat, so they don’t work as well and could also cause the vehicle to skid

Question 23

Explain velocity when an object moves in a circle

Answer 23

• If an object is travelling in a circle at a constant speed, it’s constantly changes direction so its velocity constantly changes. So, it’s accelerating
• The resultant force acts towards the centre of the circle and keeps the object moving (centripetal force)

Question 24

What’s Inertia?

Answer 24

The tendency for the motion of an object to remain unchanged
e.g. objects with large mass like the moon have a lot of inertia

Question 25

What's inertial mass?

Answer 25

How difficult it is to change an object's velocity (force/acceleration)

Question 26

What's the stopping distance?

Answer 26

distance between the driver spotting a hazard and the vehicle coming to a complete stop: Thinking distance + braking distance

Question 27

What's the thinking distance? - what is it affected by?

Answer 27

The distance the car travels in the time between noticing the hazard and applying the brakes, affected by: - Reaction time increased by tiredness, alcohol, drugs... - speed: the faster you're going the further you'll travel during reaction time

Question 28

What's the braking distance?

Answer 28

the distance taken to stop once the brakes have been applied, affected by: - Speed - Mass - Condition of brakes - Friction between tyres and road

Question 29

Explain why the units of acceleration are m/s^2

Answer 29

velocity or speed is (measured in) m/s (1) divided by time in s (1)

Question 30

A crane is lifting a heavy block from the ground to the top of a building. Explain why the upward force from the cable during the first 2 s is greater than the upward force for the next 4 s.

Answer 30

- In first 2 seconds, the block is accelerating which requires a resultant force - In the next 4 seconds, the forces are balanced because velocity is constant