# Physics

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 Author: Mathu ID: 259037 Filename: Physics Updated: 2014-01-29 11:13:24 Tags: mechanics revise Folders: unit 1 Description: velocity and displacement Show Answers:

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1. Define an objects instantaneous speed?
the speed at a given instant of time
2. How to work out average speed?
Average speed= (distance travelled)/(time taken)
3. When is an object in uniform motion?
and give two quantities which describe this motion.
• When an  object is moving at a steady speed in a straight line.
• displacement and velocity.
4. Define displacement and velocity?
• Displacement: the distance it has travelled in a particular direction.
• Velocity: Its speed in a particular direction
5. Give the equation used to work out veloctiy?
velocity=(displacement)/(time)

• (the velocity of an object is the rate of change of its displacement).
6. state si unit for displacement or distance measured in, time and velocity ?
• Velocity measured in= metres per secound ()
• Displacement or distance measured in= metres(m).
• Time measured in =seconds (s)
7. What is a vector quantity?
A Vector quantity has both magnitude (size) and direction (e.g: displacement, velocity)
8. define a scalar quantity?
A scalar quantity has only magnitude. ( e.g: distance, speed)

9. Describe the 3 motions that are changing on the graph?
• *The straight line sloping up shows that it is going away at a steady speed. ( positive velocity)
• *a horizontal line shows that it is stationary for a while. ( zero velocity)
• *a straight line sloping down shows that it is coming back at a steady speed. (negative velocity)
10. How would the graph look like if the object is speeding up(acceleration).
11. Describe acceleration and show how to work out acceleration. And give the unit of acceleration.
• The acceleration of an object is the rate of change of its velocity.
• Acceleration=Change in velocity/Time taken
•
• Another way of writing acceleration is
•  Acceleration= (final velocity- initial velocity)/time
•
• acceleration is given in (metres per second squared.
•      where v is the final velocity and u is the initial velocity.

12. What does an object with negative acceleration and positive acceleration suggests?
• negative acceleration: the object is slowing down. Which is sometimes referred to as a deceleration or retardation.
• Positive acceleration: means the object is speeding up.
13. What does an object with zero acceleration suggests?
the object with zero acceleration either has a uniform velocity(steady speed) or is stationary.
14. What is the average acceleration of free fall on earth? the average g?
9.81
15. Describe this velocity-time graph?
• *A straight line sloping up indicates steadily increasing speed.(uniform 'positive' acceleration)
• *A horizontal line shows steady speed ('zero acceleration')
• *A straight line sloping down shows steadily decreasing speed. (negative acceleration or deceleration)
16. What does the gradient of the velocity - time graph shows?
acceleration
17. how do you find the acceleration at any instant if the graph is a curve?
find the gradient of the tangent of the curve.
18. what does a graph with decreasing gradient shows?
• shows decreasing acceleration.
19. how do you work out the displacement from a velocity-time graph. and why does it work?
The area under the velocity-time graph gives the displacement, because it is the average speed multiplied by the travelling time.

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