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Physics · Chapter 6: Energy, work and power

Year 11 Science · About 17 minutes with activities · Turn your sound on

Chapter 6 · Energy, work and power
How fast at the bottom?no stopwatch allowed
h = 1.5 m
m = 50 kg
v = 5.42 m s⁻¹at the bottom
mass min kg
height hin m
Fw = mgweight force
speed vEk
speed 2v4 × the Ek
F = mg = 98 N
d = 0.7 m
W = 68.6 J98 N × 0.7 m
= Ep gainedmgh = 10 × 9.8 × 0.7
Slope length ✗
Height ✓against weight
d = 0, so W = 0the wall doesn’t move
F = 150 N
d = 4 m
t = 45 s
W = Fd = 600 J
P = 13.33 W600 J ÷ 45 s

Chapter 6 recap

  • Ep = mgh: the energy stored in an object above the ground. Ek = ½mv²: the energy a moving object has. To find speed, v = √(2Ek ÷ m).
  • Conservation of energy: energy cannot be created or destroyed, only transformed or transferred. With no friction, Ep = Ek, so v = √(2gh): a 1.5 m slide gives 5.42 m s⁻¹.
  • Work: W = Fd, in joules (1 J = 1 N m). Up a ramp, use the vertical height; no movement, no work. Power: P = W ÷ t, in watts.
  • Next: Chapter 7 · Circuits and charge

How fast are you going at the bottom of a slide?

Chapter 6 · About 17 minutes · sound on

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