P2.3 - Forces in action

Question 1

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

Answer 1

extension is directly proportional to the force applied

provided that the limit of proportionality is not exceeded

Question 2

What is meant by an inelastic (plastic) deformation?

Answer 2

A deformation which results in the object being permanently stretched.

Question 3

State the equation relating force, spring constant and extension. Give appropriate units

Answer 3

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

Question 4

What is Hooke’s law?

Answer 4

force applied is directly proportional to the extension of an elastic object.

Question 5

At what point does Hooke’s law no longer apply?

Answer 5

The limit of proportionality.

Question 6

What does the limit of proportionality look like on an

extension-load graph?

Answer 6

Where the graph stops being linear.

Question 7

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

Answer 7

Elastic potential energy.

Question 8

What can extension be replaced with in

the equation for spring force?

Answer 8

Compression

Question 9

What is the equation for elastic potential energy? Give SI units for all quantities involved

Answer 9

E = ½ k x2
Energy = ½ x Spring Constant x (Extension)²
Energy (J), Spring Constant (N/m), Extension(m)

Question 10

What is weight?

Answer 10

The force that acts on an object due to gravity and the object’s mass.

Question 11

What quantities does weight depend on?

Answer 11

● The object’s mass.

● The gravitational field strength at the given position in the field.

Question 12

What is the unit used for weight?

Answer 12

Newton

Question 13

What is the equation used to calculate weight?

Answer 13

Weight (N) = mass (kg) x gravitational field strength (N/kg)

Question 14

What type of field does all matter have?

Answer 14

A gravitational field.

Question 15

What is the acceleration of an object falling in free

fall with no resistive forces acting?

Answer 15

10 m/s²

Question 16

Why would your weight be different if you were on a

different planet?

Answer 16

The gravitational field strength varies

for each planet.

Question 17

What piece of equipment can be used to measure an

object’s weight?

Answer 17

A calibrated spring-balance or newton-meter.

Question 18

What is an alternative name for the turning effect of

a force?

Answer 18

A moment.

Question 19

State the equation used to calculate the moment of a force. Give appropriate units

Answer 19

Moment of force = Force x Distance

Moment (Nm), Force (N), Distance (m)

Question 20

What distance measurement is used when calculating a moment?

Answer 20

The perpendicular distance from the pivot to the line of action of the force.

Question 21

If an object is in equilibrium, what can be said about

the moments acting on the object?

Answer 21

Clockwise = anticlockwise

Question 22

What can be said about the pressure in a simple

hydraulic system?

Answer 22

The pressure in the fluid is constant through the fluid (it cannot be compressed or expand).

Question 23

Explain how a simple hydraulic lift works.

Answer 23

● The pressure is constant in the fluid.
● Force applied on each platform is equal to the product of pressure and area (F = pA).
● One platform has a larger area than the other, meaning the force produced is greater than the force applied to the smaller platform.