Mechanics and Materials (2): On the move

Question 1

What is the equation for an object moving in a circle at a constant speed?

Answer 1

v = 2(pi)R/T

Question 2

What are the two types of speeds you can calculate when an object has a changing speed?

Answer 2

Instantaneous velocity
Average velocity

Question 3

What is the equation for instantaneous velocity?

Answer 3

v = s/t at that point

Question 4

What is the equation for average velocity?

Answer 4

v = (delta)s/(delta)t

where:
delta s - total distance
delta t - total time

Question 5

What does the distance-time graph look like for an object travelling at a constant speed?

Answer 5

A straight line graph through the origin

Question 6

How do you find the speed of an object (moving at constant speed) on a displacement/distance-time graph?

Answer 6

Find the gradient of the straight line

Question 7

How do you find the instantaneous speed of an object (moving at a changing speed) on a displacement/distance-time graph?

Answer 7

Draw a tangent at the point that you want to know the speed for and calculate the gradient of that line

Question 8

What is the definition of constant velocity?

Answer 8

When an object moves with the same speed without changing its direction of motion

Question 9

Does an object moving in a circular path have a constant velocity?

Answer 9

NO, as its direction is constantly changing

Question 10

Can displacement have both a +ve and -ve sign?

Answer 10

Yes

Question 11

What is the definition of acceleration?

Answer 11

The change in velocity per unit time

Question 12

Is acceleration a scalar or vector quantity?

Answer 12

Vector (they can have a negative or positive value for deceleration or acceleration)

Question 13

What is the definition of uniform acceleration?

Answer 13

When the rate of change of velocity of an object is constant

Question 14

What is the equation for uniform acceleration?

Answer 14

a = v-u/t

Question 15

What type of graphs display acceleration as the gradient?

Answer 15

Velocity-time graphs

Question 16

What is the definition of non-uniform acceleration?

Answer 16

When the rate of change of velocity of an object is not constant

Question 17

How do you find the acceleration at a point on a velocity-time graph if the acceleration is not constant?

Answer 17

Draw a tangent at that point and find the gradient of it

Question 18

In what scenario can you use suvat equations?

Answer 18

When the acceleration is constant

Question 19

How do you find the displacement from a velocity-time graph?

Answer 19

displacement = area under the graph

Question 20

What is theoretical way that you can determine the acceleration due to gravity?

Answer 20

Make a multi flash photo or video clip of the balls flight as it falls after being released from rest.
- The flashing light needs to flash at a known constant rate
- After you have collected the data you can slow the video down and record the time taken to travel each distance

Question 21

What is acceleration of free fall?

Answer 21

When acceleration of an object is due to no other factor apart from the weight of an object

Question 22

What is the value of acceleration of free fall?

Answer 22

9.81 ms^-1

Question 23

Why is it unusual to get acceleration of free fall?

Answer 23

Due to air resistance acting on the body that is falling

Question 24

What is the practical way we used to determine the value of g?

Answer 24

EQUIPMENT:
- Stand and Clamp
- Electromagnet
- Steel ball bearing
- Light gate connected to stopwatch

METHOD
- Set up the apparatus with the electromagnet at the highest point on the clamp and then two light gates one higher and one lower (the position of the lower light gate should be adjusted to a known height)
- Determine the height between the two light gates
- Turn on the electromagnet and attach the steel ball bearing to it
- Turn off the electromagnet, releasing the ball bearing and record the time taken for the ball to fall between the 2 light gates
- Reduce the height between the 2 light gates by 50 cm each time and doing three repeats for each height
- Determine the average time taken for the steel ball to fall between the two light gates

ANALYSIS
- h = ut + 1/2gt^2
- Plot a graph of h against t^2 against height and your gradient will = 2g

SAFETY
- A suitable container should be placed under the trapdoor to catch the ball bearing to prevent it from falling on the floor and creating a trip hazard
- Use a counterweight or clamp on the stand to avoid it falling over and causing injury

Question 25

If a ball is dropped into sand describe what values change as the ball hits the sand

Answer 25

- Initial acceleration is g downwards - When the ball reaches the sand it decelerates and so the value of acceleration is no longer g NB: The link between the two stages is that the final velocity before the ball hits the sand is its initial velocity when the ball hits the sand

Question 26

When doing a question involving projectiles and movement what is the first thing that you should do?

Answer 26

Define which way is positive and negative - Normally up and right is defined as positive

Question 27

What are the signs of the values for velocity and acceleration when an object is moving forwards and accelerating?

Answer 27

Velocity = +ve Acceleration = +ve

Question 28

What are the signs of the values for velocity and acceleration when an object is moving forwards and decelerating?

Answer 28

Velocity = +ve Acceleration = -ve

Question 29

What are the signs of the values for velocity and acceleration when an object is moving backwards and decelerating?

Answer 29

Velocity = -ve Acceleration = +ve

Question 30

What are the signs of the values for velocity and acceleration when an object is moving backwards and accelerating?

Answer 30

Velocity = -ve Acceleration = -ve

Question 31

The vertical and horizontal components of a projectile are...?

Answer 31

Independent

Question 32

What is the definition of a projectile?

Answer 32

An object acted upon only by the force of gravity

Question 33

In projectiles what is the vertical acceleration of the object equal to?

Answer 33

g (always negative as it is acting downwards)

Question 34

The horizontal velocity of a projectile is...?

Answer 34

Constant

Question 35

Describe the velocity-time graph for an object projected vertically.

Answer 35

- You have both negative and positive velocity as the value is a vector The graph begins at a positive maximum as it is thrown up into the air. The velocity decreases at a constant rate (STRAIGHT LINE) until it reaches its maximum height where velocity = 0. The velocity then goes into the negative portion of the graph increasing at a constant rate again (STRAIGHT LINE) until it reaches its maximum velocity again

Question 36

For an object projected horizontally, how does its vertical path change as time progresses?

Answer 36

The vertical distance the object travels in a given time increases as time progresses

Question 37

For an object projected horizontally, how will changing the speed that it is projected at change its motion?

Answer 37

The object will be projected further

Question 38

Does projecting an object faster horizontally change how long it takes for the object to reach the ground?

Answer 38

No

Question 39

What apparatus can you use to measure compare horizontal versus vertical projection?

Answer 39

A stroboscope and camera with a slow shutter - this will capture photos of the two balls' motions as they are projected

Question 40

For a component projected horizontally, what is its horizontal displacement at time, t, after being projected with initial velocity, u?

Answer 40

sx = ut (as the object does not accelerate horizontally)

Question 41

For a component projected horizontally, what is its vertical displacement at time, t, after being projected with initial velocity, u?

Answer 41

sy = 1/2gt^2 (as the object has no initial vertical velocity)

Question 42

What are two examples of projectile motion that aren't to do with projecting a ball into air?

Answer 42

- Path of a ball rolled across an inclined plane - Path of an electron between two charged plates -> Its motion parallel to the plates is at 0 acceleration but the acceleration of each electron is the same and constant towards the positively charged plate

Question 43

What is the definition of friction?

Answer 43

A resistive force that opposes the motion of an object turning the kinetic energy of objects into other energy sources such as heat or sound

Question 44

What is the name of the resistive force that opposes the motion of projectiles?

Answer 44

Drag/air resistance

Question 45

What characteristic increases the value of drag/air resistance?

Answer 45

- Speed of the object

Question 46

What is the name of the upwards force that acts opposite to air resistance?

Answer 46

Lift

Question 47

How does air resistance effect the horizontal components of a projectile?

Answer 47

Air resistance has a horizontal component that reduces both the horizontal speed of the projectile and its range

Question 48

How does air resistance effect the vertical components of a projectile?

Answer 48

If the initial projection of the projectile is above the horizontal then the maximum height it reaches will be lower due to air resistance. Also its descent will be steeper.

Question 49

How can the shape of a projectile affect whether it experiences a life force due to air resistance e.g shape of an aircraft wing?

Answer 49

- This happens if the shape of the projectile causes air to flow faster over the top and slower under the bottom - This causes a the pressure on the top surface to be less than the pressure on the bottom surface - The pressure difference causes a lift force