P9 - Motion

Question 1

What is speed? What is the equation for speed?

Answer 1

Speed is the magnitude of velocity. SCALAR

Speed = Distance / Time

s = d / t

(m/s) = (m) / (s)

Question 2

How can the speed equation be rearranged?

Answer 2

s = d / t

Rearranged:

• d = s x t
• t = d / s

Question 3

What are some commonly used speed units?

Answer 3

m/s, mph, km/h, km/s etc…

Question 4

What is the purpose of a Distance-Time Graph? How can you calculate the speed?

Answer 4

To show the relationship between distance and time for a particular journey.

You can work out the speed of the object by calculating the gradient, m:

change in y / change in x

Question 5

What does a horizontal line on a DT graph show?

Answer 5

Object is stationary

Question 6

What does an upwards diagonal line on a DT graph show? What does its gradient tell us?

Answer 6

Object is at a constant speed.

Steep gradient = faster constant speed

Question 7

What does a downwards diagonal line on a DT graph show?

Answer 7

Object is moving at a constant speed - in the opposite direction (back to the start).

Question 8

What does the gradient on a DT graph show?

Answer 8

The speed

s = d/t

Question 8

What is acceleration?

Answer 8

A measure of how quickly velocity changes.

speed up = positive acceleration
slowing down = negative acceleration (deceleration)

Vector - magnitude and direction.

Question 10

What is the unit for acceleration?

Answer 10

m/s^2

Question 11

What is velocity? How is it different to speed?

Answer 11

The *speed of an object in a given direction and a given time. VECTOR

*speed is the magnitude of velocity without a direction. Speed tells us how fast something is moving without giving us information about whether it is speeding up, slowing down or constant.

Question 12

What is the equation for acceleration?

Answer 12

Acceleration = (Final velocity - Initial Velocity) / Time taken

A = V - U / T

Question 14

What is the alternative calculation for acceleration which uses distance in the equation?

Answer 14

Final Velocity - Initial Velocity = 2 x acceleration x distance (s).

V^2 - U^2 = 2as

Use this equation when the question requires distance as a variable.

E.g V = square root of (2as + U^2)

Question 15

What is Deceleration?

Answer 15

Deceleration is negative acceleration - when an object slows down.

Question 15

Give some other SUVAT equations?

Answer 15

s = 1/2 (u + v) t

v^2 = u^2 + 2as

s = ut + 1/2 at^2

v = u + at

Question 16

What is the purpose of a Velocity-Time Graph?

Answer 16

To show how fast the object is travelling and whether the object is accelerating or decelerating.

Question 17

What does a horizontal line on a VT graph show?

Answer 17

Object is moving at a constant speed.

constant speed = 0 acceleration

Question 18

What does a straight upwards diagonal line on a VT graph show?

Answer 18

Object is accelerating at a constant rate.

The steeper the gradient, the faster the rate of acceleration.

Question 19

What does a straight downwards diagonal line on a VT graph show?

Answer 19

Object is decelerating at a constant rate.

The steeper the gradient, the faster the rate of deceleration.

Question 21

What does a curved line on a VT graph show?

Answer 21

Changes in velocity not at a constant rate - i.e sudden acceleration or deceleration.

Question 22

How do you calculate the distance travelled on a VT graph?

Answer 22

Find the area of the space under the graph.

Question 22

How do you calculate the acceleration on a VT graph?

Answer 22

If the line is straight:
-find the gradient in the normal way - change in velocity (y) / change in time (x)

If the line is curved:
-draw a tangent at the certain point in time - calculate the gradient of the tangent.

Question 24

When describing the motion of an object, what should you do?

Answer 24

Divide the graph into 3 sections and comment on the motion at:

1) the beginning
2) the middle
3) the end

Question 25

What are the speed values (m/s) for light, sound, walking, running and cycling?

Answer 25

Light - 300,000,000 m/s
Sound - 330 m/s

• Walking - 1.5 m/s
• Running - 3 m/s
• Cycling - 6 m/s

*Roughly doubles