Section 5: Mechanics

Question 1

What’s the difference between a scalar and a vector?

Answer 1

A scalar quantity has only size, while a vector quantity has size and direction.

Question 2

What name is given to a vector formed by adding vectors together?

Answer 2

The resultant vector

Question 3

Give an example of 3 vectors.

Answer 3

Displacement, velocity, force, acceleration or momentum

Question 4

Give an example of 3 scalars.

Answer 4

Any 3 from: length, distance, speed, mass, temperature, time or energy

Question 5

If a body is in equilibrium, what’s the sum of all the forces acting on it?

Answer 5

0

Question 6

Explain what equilibrium means in the context of a moving object

Answer 6

The sum of all the forces acting on a body in equilibrium is 0

Question 7

What is a moment?

Answer 7

A moment is the turning effect of a force around a turning point.

Question 8

What name is given to a pair of forces of equal size which act parallel to each other, in opposite directions?

Answer 8

A couple

Question 9

What is the centre of mass of an object?

Answer 9

The centre of mass of an object is the single point that you can consider its whole weight to act through

Question 10

Where is the centre of mass in a uniform regular solid

Answer 10

At the centre of an object

Question 11

What’s the velocity of an object?

Answer 11

The rate of change of displacement

Question 12

What’s the acceleration of an object?

Answer 12

The rat of change of velocity

Question 13

What does SUVAT stand for? Give the units for each measurement.

Answer 13

S- Displacement (in m)
U- Initial Velocity (in ms^-1)
V- Final Velocity (in ms^-1)
A- Acceleration (in msˉ²)
T- Time (in s)

Question 14

What kind of motion does a curved displacement-time graph show?

Answer 14

Acceleration or deceleration

Question 15

What kind of motion does a straight line show on a displacement-time graph?

Answer 15

Constant velocity

Question 16

What does the rate of change of gradient on a displacement-time graph represent?

Answer 16

Distance

Question 17

How would you calculate the average velocity of a moving object with non-uniform acceleration using a displacement-time graph?

Answer 17

Divide the overall change in displacement by the time taken

Question 18

What is the difference between average and instantaneous velocity?

Answer 18

Instantaneous velocity is an object’s velocity at a particular moment in time, average velocity is the overall displacement divided by time taken

Question 19

What does the gradient of a velocity-time graph tell you?

Answer 19

Acceleration

Question 20

How is uniform acceleration shown on a velocity-time graph?

Answer 20

A straight line

Question 21

What does the area under a velocity-time graph tell you?

Answer 21

The displacement

Question 22

How is non-uniform acceleration shown on a velocity-time graph?

Answer 22

A curved line

Question 23

How would you find velocity from an acceleration-time graph?

Answer 23

The area under the graph

Question 24

How would constant velocity appear on an acceleration-time graph?

Answer 24

Constant velocity means acceleration is zero, so it would appear as a straight horizontal line through 0 on the vertical axis.

Question 25

What does negative acceleration on an acceleration-time graph show?

Answer 25

Decleration

Question 26

State Newton’s first law of motion.

Answer 26

“The velocity of an object will not change unless a resultant force acts on it.”

Question 27

State Newton’s second law of motion

Answer 27

Newton’s second law states that the acceleration of an object is proportional to the resultant force acting on it. This can be shown as: F= m x a
F- Force (in N)
m- Mass (in Kg)
a- Acceleration (in ms^-2)

Question 28

State Newton’s third law of motion

Answer 28

“If an object A exerts a force on object B, then the object B exerts an equal but opposite force on object A.”

Question 29

What’s the only force present in free-fall motion?

Answer 29

Weight

Question 30

What’s freefall motion called when the object is given an initial velocity

Answer 30

Projectile motion

Question 31

What is the effect of air resistance on the trajectory of a projectile?

Answer 31

Air resistance causes a drag force that acts in the opposite direction to motion and affects the trajectory of a projectile, The horizontal component of drag reduces the horizontal speed of the projectile, and reduces the horizontal distance the projectile can travel. If the projectile has a vertical component of velocity, drag reduces the maximum height the projectile will reach, and steepens the angle of descent.

Question 32

What is meant by friction and drag?

Answer 32

Friction is a force that acts opposite to motion. Drag is the name given to friction caused by a fluid.

Question 33

In what direction does a frictional force act?

Answer 33

Opposite direction to motion

Question 34

In what direction does a lift force act, relative to a flowing fluid?

Answer 34

Lift acts perpendicular to the direction the fluid is flowing

Question 35

What can you say about the frictional forces and the driving forces acting on an object when it reaches terminal velocity?

Answer 35

When an object reaches terminal velocity, the frictional forces are equal in size to the total driving force and in the opposite direction

Question 36

What is the difference between an elastic and inelastic collision?

Answer 36

An elastic collision is one where linear momentum and kinetic energy is conserved. An inelastic collision is one where linear momentum is conserved but kinetic energy is not