P2 2 Forces

Question 0

What is the unit of a force?

Answer 0

The Newton (N).

Question 1

What can a force do?

Answer 1

A force can change the shape of an object or change its motion or its state of rest.

Question 2

What happens when two forces interact?

Answer 2

When two forces interact, they always exert equal and opposite forces on each other.

Question 3

What happens to a boxer who exerts a punch of 100 N on an opponent?

Answer 3

The boxer experiences a reverse force of 100N.

Question 4

What is the resultant force?

Answer 4

The resultant force is a single force that has the same effect as all the forces acting on an object.

Question 5

What does it mean when the resultant force is zero?

Answer 5

The object stays at rest or at constant velocity. If the resultant force of an object is not zero, the velocity of the object will change.

Question 6

Forces and resultant force

Answer 6

When two forces act on the same line, the resultant force is their sum if they go in the same direction and their difference if they go in opposite directions.

Question 7

What happens to acceleration if the resultant force increases?

Answer 7

Acceleration increases too.

Question 8

Important equation

Answer 8

F = ma

Resultant force N = mass kg x acceleration m/s^2

Question 9

Fill the gap

The greater the mass of an object, the … the acceleration for a given force

Answer 9

Smaller.

Question 10

Stopping distance=

Answer 10

Thinking distance + braking distance.

Question 11

What is the thinking distance?

Answer 11

The distance travelled by the vehicle in the time it takes the driver to react (ie during the driver’s reaction time).

Question 12

What is the braking distance?

Answer 12

The braking distance is the distance travelled by the vehicle during the time the braking force acts.

Question 13

What increases the thinking distance?

Answer 13

The thinking distance is increased due to
•Tiredness
•Alcohol
•Drugs

Question 14

What increases the braking distance?

Answer 14

The braking distance is increased by
•Adverse road conditions, Eg: rain and snow
•The faster a vehicle is travelling
•Faulty car brakes
•Worn out tyres

Question 15

What is the weight and mass of an object?

Answer 15

The weight of an object is the force of gravity on it.

The mass of an object is the amount of matter in it.

Question 16

Weight equation

Answer 16

Weight N = mass kg x gravitational field strength N/kg

Or W = mg

Question 17

What happens when an object falls in a fluid?

Answer 17

When an object falls in a fluid, the fluid drags on the object. The drag force increases with speed. The object then reaches a constant velocity where the weight is equal to the resistive forces. This is called terminal velocity. The resultant force is zero.

Question 18

Elastic objects

Answer 18

An elastic object regains its original shape when the forces deforming it are removed.

Question 19

How to calculate the extension of a spring

Answer 19

The extension of the strip of material at any stage = its length at the stage - the original length.

Question 20

What happens when an elastic object is stretched?

Answer 20

When an elastic object is stretched, elastic potential energy is stored in the object. This is because work is done on the object by the stretching force.

Question 21

What does Hooke’s law state?

Answer 21

Hooke’s law states that the extension of a spring is directly proportional to the force applied, provided its limit of proportionality is not exceeded.

Question 22

Hooke’s law equation

Answer 22

Force applied N = spring constant N/m x extension m.

Or F = k x e.

Question 23

Anti skid surfaces

Answer 23

The surface is tougher than normal. This causes more friction between the surface and the car’s tyre.