P4 revision

Question 1

When an object moves in a straight line at a steady speed, you can calculate its average speed if you know how far it travels and how long it takes. What is the formula for calculating speed?

Answer 1

distance moved
average speed = ———————–
time taken

Question 2

Average speed is measured in?

Answer 2

metres per second

Question 3

Distance moved is measured in?

Answer 3

metres

Question 4

Time taken is measured in?

Answer 4

seconds

Question 5

What does a distance/time graph show?

Answer 5

A distance-time graph shows how far something travels over a period of time.When an object is stationary, the line on the graph is horizontal. When an object is moving at a steady speed in a straight line, the line on the graph is straight but sloped.Note that the steeper the line, the faster the object is travelling.

Question 6

What does velocity mean?

Answer 6

The velocity of an object is its speed in a particular direction.

Question 7

A velocity-time graph shows the speed and direction an object travels over a specific period of time. Velocity-time graphs are also called speed-time graphs. What would the line on a graph look like if an object is travelling at a constant speed?

Answer 7

The line on the graph is horizontal. When the line is at zero velocity the object is at rest.

Question 8

When an object is undergoing constant acceleration?

Answer 8

The line on the graph is straight but sloped, (in an upward direction.) The steeper the line, the greater the acceleration of the object.

Question 9

With a constant deceleration?

Answer 9

The line on the graph is straight but sloped, in a downward direction (with a negative gradient).

Question 10

Acceleration can be calculated by?

Answer 10

change in velocity (m/s) ÷ time taken (s)

Question 11

What are the two main forces which affect a falling object at different stages of its fall?

Answer 11

The weight of the object - this is a force acting downwards, caused by the Earth’s gravitational field acting on the object’s mass.
Air resistance - this is a frictional force acting in the opposite direction to the movement of the object. (Note that in space and other vacuums there is no air resistance.)

Question 12

What is meant by terminal velocity?

Answer 12

When the object’s weight is balanced by the air resistance. There is no resultant force and the object reaches a steady speed – this is known as the terminal velocity.

Question 13

What is air resistance?

Answer 13

This is a frictional force acting in the opposite direction to the movement of the object. (Note that in space and other vacuums there is no air resistance.) It decreases the velocity of an object.

Question 14

The factors affecting the terminal velocity of an object include:

Answer 14

• • its mass
• • its surface area
• • the acceleration due to gravity, g

Question 15

What is thrust? What does it do?

Answer 15

Thrust - increases the velocity of an object.

Question 16

What is a unit of force called?

Answer 16

Newton (N)

Question 17

What is 1 Newton approximately equal to?

Answer 17

1 newton is defined as that unbalanced force which produces an acceleration of 1 m/s2 when it acts on a mass of 1 kg. An average-sized apple weighs about 1 newton.

Question 18

What is friction?

Answer 18

It is the force that opposes motion.

Question 19

How does a surface affect the friction?

Answer 19

The greater the forces needed to pull an object, the higher the friction. For example, more friction is usually seen when pulling a block across sandpaper. Covering a table with plastic usually reduces the friction.