P2.3 Forces In Action

Question 1

Momentum equations

Answer 1

Momentum(p) = mass(m) x velocity(v)

Equation for final velocity after a collision:
m1v1 + m2v2 = (m1 + m2) * vfinal

m = mass
v = velocity
vfinal = final combined velocity of both objects after the collision

Question 2

Kg into Newtons

Answer 2

1kg = 10N

10N is earth gravitational field strength (N/kg) represented by g

Question 3

Explain relationship between force applied and extension of an elastic object.

Answer 3

Extension is directly proportional to the force applied, provided that the limit of proportionality is not exceeded

Question 4

Inelastic deformation

Answer 4

Deformation which results in the object being permanently stretched
Object doesn’t return to its original shape when the force is removed

Question 5

Equation relating force, spring constant and extension

Answer 5

Force = Spring Constant x Extension
F = kx
Force (N), Spring Constant (N/m), Extension (m)

NB: spring constant is how STIFF a spring is - large value = more stiff

Question 6

Hooke’s law

Answer 6

Force applied is DIRECTLY PROPORTIONAL to extension of an elastic object

Question 7

At what point does Hooke’s law no longer apply

Answer 7

The limit of proportionality.

Question 8

What does the limit of proportionality look like on an extension-load graph?

Answer 8

Where the graph stops being linear
| _—————
| /‾ <—— The graph stops being linear here
| /
|/_______________

Question 9

What type of energy is stored in a spring when it is stretched

Answer 9

Elastic potential energy

Question 10

What can extension be replaced with in the equation for spring force

Answer 10

Compression

Question 11

Equation for elastic potential energy

Answer 11

Energy (J) = ½ × Spring Constant (N/m) × (Extension (m))²

Question 12

Weight

Answer 12

Force that acts on an object due to gravity and the object’s mass
Weight (N) = mass (kg) x gravitational field strength (N/kg) (10N/kg on earth)

Question 13

What quantities does weight depend on

Answer 13

Object’s mass
Gravitational field strength at the given position in the field

Question 14

What is meant by an object’s centre of mass

Answer 14

Single point through which an object’s weight can be considered to act through

Question 15

What type of field does all matter have

Answer 15

Gravitational field

Question 16

How does the gravitational field of an object change as the object becomes more massive

Answer 16

Field strength increases

Question 17

Acceleration of an object falling in free fall with no resistive forces acting

Answer 17

10 m/s²

Question 18

Why would your weight be different if you were on a different planet

Answer 18

Gravitational field strength varies for each planet
Weight is the product of mass and gravitational field strength

Question 19

What piece of equipment can be used to measure an object’s weight

Answer 19

Calibrated spring-balance or newton-meter

Question 20

Alternative name for the turning effect of a force

Answer 20

Moment

Question 21

Equation used to calculate the moment of a force

Answer 21

Moment of force (Nm) = Force (N) × Distance (m)

Question 22

What distance measurement is used when calculating a moment

Answer 22

Perpendicular distance from the pivot to the line of action of the force

Question 23

If an object is in equilibrium, what can be said about the moments acting on the object

Answer 23

Clockwise moments are equal to the anticlockwise moments

Question 24

What does the direction of a resultant moment acting on an object tell you

Answer 24

Direction that object will rotate around pivot point

Question 25

In any fluid, at what angle do the forces due to pressure act on a given surface

Answer 25

Right angles (normal to) the surface

Question 26

What can be said about the pressure in a simple hydraulic system

Answer 26

Pressure in the fluid is constant through the fluid (it cannot be compressed or expand)

Question 27

How a simple hydraulic lift works

Answer 27

Pressure is constant in fluids
Force applied on each platform is equal to the product of pressure and area (F = p x A).
One platform has a larger area than the other, meaning the force produced is greater than the force applied to the smaller platform

Question 28

Equation for gravitational potential energy

Answer 28

GPE = mass x gravitational field strength x height