Module 3: Forces And Motion

Question 1

When can you use SUVAT equations

Answer 1

When there is uniform acceleration.

Question 2

What is the normal contact force relative to the surface?

Answer 2

Perpendicular.

Question 3

What is the friction relative to the surface?

Answer 3

Parallel.

Question 4

What is the relationship between normal contact force and friction

Answer 4

F=μN

Question 5

What is tension and what are the assumptions made when answering a question involving it?

Answer 5

Tension is the force exerted by a rope, cable or a similar object.

Tension is the same throughout a cable if you assume that the cable doesn’t have a mass and doesn’t stretch.

Question 6

What is the centre of mass of an object?

Answer 6

The point on an object where a single force doesn’t have a turning effect.

Question 7

What is the centre of gravity of an object?

Answer 7

The point on an object where weight appears to act.

Question 8

What does it mean when an object is uniform?

Answer 8

It’s centre of gravity is in the middle

Question 9

What is Newton’s first law?

Answer 9

That an object will remain at rest or continue to move with a constant velocity unless acted upon by a resultant force (law of inertia).

Question 10

What is Newton’s second law?

Answer 10

That the resultant force acting on an object is directly proportional to the rate of change of momentum, where the change in momentum occurs in the same direction as the resultant force.

Question 11

What is Newton’s third law?

Answer 11

That when one body exerts a force on a second body, the second body simultaneously exerts an equal and opposite force on the first body

Question 12

What are the conditions for dynamic equilibrium?

Answer 12

Dynamic equilibrium can only occur if the object is in translational and rotational equilibrium.

Question 13

Define a moment.

Answer 13

The product of the force and the perpendicular distance from the pivot.

Question 14

Define a couple and torque.

Answer 14

A couple is a pair of equal and opposite forces of magnitude F with their line of action separated by a distance d.

Torque is the moment of couple, and is defined as the product of one of the forces and the perpendicular distance between them, Torque = Fd.

Question 15

What is the principle of moments?

Answer 15

For a body in rotational equilibrium, the sum of the anticlockwise moments is equal to the sum of the clockwise moments about that point.

Question 16

State the principle of conservation of momentum?

Answer 16

Momentum is always conserved in a closed system.

Question 17

What is the difference between elastic and inelastic collisions?

Answer 17

Both collisions conserve total energy and momentum, but in elastic collisions, kinetic energy is also conserved.

Question 18

What is impulse?

Answer 18

The product of a force and the time this force acts on an object, therefore, impulse = change in momentum, Δp=fΔt.

Question 19

What is the relationship between drag and speed?

Answer 19

Drag ∝ speed².

Question 20

When does an object reach terminal velocity?

Answer 20

Terminal velocity occurs when drag and acceleration due to gravity are equal.

Question 21

Define pressure.

Answer 21

The normal contact exerted per unit cross-sectional area.

Question 22

What is the equation for pressure in a fluid?

Answer 22

P = ρhg, pressure = density of the fluid x height of object x g.

Question 23

State Archimedes principle?

Answer 23

The upthrust exerted on an object submerged in a fluid is equal to the weight of the displaced fluid, regardless of whether or not the object is partially or fully submerged.

Question 24

When fully submerged…

Answer 24

Volume of the object = Volume of displaced fluid.

Question 25

When partially submerged…

Answer 25

Mass of object = Mass of displaced fluid

Question 26

What is work done?

Answer 26

The product of the component of the force in the same direction as motion and distance travelled, W=Fscosθ

Question 27

What is the principle of conservation of energy?

Answer 27

Total energy in a closed system stays constant. Energy can’t be created or destroyed, only transferred.

Question 28

What is power?

Answer 28

The rate of work done / energy transferred.

Question 29

Power = …

Answer 29

E/t, energy over time.
Fv, force x velocity, as long as the force is constant.