Unit 2 Thermal physics
Notes
Example 4c (iv)
An athlete exerts an average horizontal force on the ground of 30N while running. She runs a distance of 1.6km in 5.0 minutes.
 State the equation linking work, force and distance.
 Calculate the work the athlete does.
 State the equation linking power, work done (or energy transferred) and time taken.
 Calculate the power of the athlete.
Answer
 work done = force × distance moved or W = F × d

Step 1 List all the information in symbol form and change into appropriate and consistent SI units if required.
F=30N
d=1.6km=1600m
W=?
Step 2 Calculate the answer by putting the numbers into the equation.
W= 30 × 1600=48000J 
power = work done
time taken= energy transferred
time takenor P= W
t= E
tpower = work done
time taken= energy transferred
time takenor P = W
t= E
t 
Step 1 List all the information in symbol form and change into appropriate and consistent SI units if required.
W=48000J
t=5.0 × 60s=300s
P=?
Step 2 Calculate the answer by putting the numbers into the equation.
P= 48000
300=160W ALWAYS REMEMBER TO STATE THE UNIT FOR CALCULATED QUANTITIES.