Edexcel A-Level Physics Conservation of Energy

Practise Edexcel A-Level Physics conservation of energy through GPE-KE transfers, dissipated work, friction effects, loops, slopes and bungee contexts.

Exam points

equate loss of gravitational potential energy to kinetic energy or useful work
include dissipated energy from friction, drag or braking when applying energy conservation
judge whether an object completes a loop or reaches a height from available energy

[Maximum number: 5]

The luge is an event at the Winter Olympics. An athlete lies on a small sledge and races down an icy track, feet first.

Figure for Question 1.3.20 - Conservation of energy question 1 — Edexcel A-Level Physics AS

After the finish line there is a straight, uphill section of track for the sledge to decelerate in. The maximum permitted gradient of this section is 20%.

An athlete reaches the finish line at a velocity of $33 \mathrm{~m} \mathrm{~s}^{-1}$ . She then applies a minimum braking force of 240 N as she moves along the uphill section of track to help her come to a stop.

Calculate the minimum uphill length of track L that should be available for braking. You should ignore all frictional forces other than those applied by the athlete.
mass of sledge and athlete $=95 \mathrm{~kg}$

Either (energy)

Use of $E_k=\frac{1}{2}mv^2$ .

Use trigonometry to determine the component of weight along the slope or the vertical height in terms of L.

Use of $E_{grav}=mg\Delta h$ to determine gravitational energy, or use of W=Fs.

Use of $E_k=E_{grav}+W$ to determine $L=120\,\mathrm{m}$ .

Or (forces)

Use trigonometry to determine the component of weight along the slope or the vertical height in terms of L.

Use of resultant force = $mg\sin 11.3^{\circ}+240\,\mathrm{N}$ .

Use F=ma to determine a.

Use of $v^2=u^2+2as$ with their a (not 9.81) to determine s.

$L=120\,\mathrm{m}$ . Example: $L=122\,\mathrm{m}$ .

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1.3.20 - Conservation of energy question 1