Mechanics

Question 1

What is instantaneous velocity?

Answer 1

Velocity at a particular point in time

Question 2

How can we find the instantaneous velocity from a displacement time graph?

Answer 2

Draw a tangent on the graph and work out the gradient of that point

Question 3

What are the suvat equations?

Answer 3

v=u+at
v^2=u^2+2as
s=ut+1/2at^2
s=1/2(u+v)t

Question 4

How can we find the acceleration of free fall?
(practical)

Answer 4

• drop marble from different heights and record time it takes to reach the ground
• measure the height with a ruler
• measure the time with a stopwatch
• plot a graph of h against t^2 because of s=ut + 1/2at^2, a half of acceleration will be the gradient since s=1/2at^2

Question 5

How can we reduce uncertainty?

Answer 5

Make sure h is a large as possible and use trapdoor, where ball is held by electromagnet, or use a light gate

Question 6

What is stopping distance?

Answer 6

thinking distance+braking distance

Question 7

What is thinking distance?

Answer 7

distance traveled by the vehicle from the moment a driver spots a hazard to the time they press the brake

Question 8

What is the braking distance?

Answer 8

The distance travelled from the moment the driver presses the brake to the moment the car stops

Question 9

What is thinking distance dependent on?

Answer 9

alcohol , drugs and tiredness

Question 10

What is braking distance dependent on?

Answer 10

conditions of tires, mass of vehicle and conditions of the road

Question 11

Is vertical component constant?

Answer 11

No, when it reaches maximum height, the vertical velocity is 0

Question 12

Is horizontal component constant?

Answer 12

yes

Question 13

What is a newton?

Answer 13

The force required to accelerate a mass of 1kg by one ms^-2

Question 14

What is tension equal to?

Answer 14

ma+mg

Question 15

When does an object experience drag?

Answer 15

When it travels through fluid

Question 16

What is drag directly proportional to?

Answer 16

velocity^2

Question 17

Describe the motion of a skydiver.

Answer 17

At first, the acceleration is g, as time increases, drag increases and acceleration decreases, after terminal velocity is reached and drag force is equal to weight, so net force is 0

Question 18

What direction is the weight acting and the normal reaction on a box on a slope?

Answer 18

The normal reaction is acting 90 degrees to the slope and the weight is acting vertically downwards

Question 19

What is the parallel component?

Answer 19

mgsintheta

Question 20

What is the perpendicular component?

Answer 20

mgcostheta

Question 21

What is the centre of mass?

Answer 21

Where the entire mass of the object seems to act

Question 22

What is the centre of gravity?

Answer 22

The point at which the entire weight of an object seems to act

Question 23

How can we find the centre of gravity?

Answer 23

• pin object and hang a plumb line
• rotate the object and pin it to a different point, hang a plumb line and mark again
• repeat this
• the intersection of those lines is the centre of gravity

Question 24

What is a moment

Answer 24

the product of force and perpendicular distance from the pivot to the line of action of the force, m=fx

Question 25

What is the principle of moments?

Answer 25

An object will be in equilibrium if:
- there is no net force acting on the object
- the sum of the anticlockwise moments is equal to the sum of the clockwise moments

Question 26

What is a torque?

Answer 26

A force couple consisting of two equal opposite forces acting in the same plane

Question 27

When is the triangle of forces true?

Answer 27

only if the object is in equilibrium

Question 28

What are the units of density?

Answer 28

kgm^3

Question 29

What are the units of pressure?

Answer 29

Nm^2, pascal

Question 30

Pressure

Answer 30

F/A, or density times height times g

Question 31

Archimedes principal

Answer 31

the upthrust acting on a body submerged in a liquid is equal to the weight of the liquid that has been displaced