4- Work, energy and power

Question 1

moments

Answer 1

• F*d

- in balance, clockwise/anti-clockwise moments need to cancel out

Question 2

work

Answer 2

• F* displacement = work done (J)
• is actually a scalar quantity
• work done in any direction other than the direction of the force must be written as a product of its vertical/horizontal components (right-angled triangle)
• if an object has the capability to do work it has energy

Question 3

Gravitational potential energy

Answer 3

• massgheight = G.P.E (J)

- mass*g is also weight

Question 4

Kinetic energy

Answer 4

• 1/2massvelocity^2

Question 5

Elastic potential energy

Answer 5

-1/2Forceextension^2

Question 6

pendulums

Answer 6

• at max points of swing, all K.E has transferred to G.P.E, gravity pulls it back to minimum points
• at minimum points of swing, all G.P.E has converted to K.E, momentum carries it on up to maximum points
• in a non-closed system pendulum slowly loses energy to work done against air resistance and sound (internal energy)

Question 7

conservation of energy

Answer 7

• all energy is always used in a system, although some is often more useful than others, so the non-useful energy can be considered wasted
• efficiency is useful energy gotten out of total input as a percentage
• wasted energy is often given as an increase in potential energy and kinetic energy of surrounding particles

Question 8

power

Answer 8

• work done or energy transferred/ time taken=power (W)
• rate at which energy is transferred
• also retarding force being overcome * speed
• 1 horsepower = 746 watts