Homework 3.1
Skydiving
The physics of skydiving, an exciting sport involving free fall from a plane or balloon and the use of a
parachute, has been described in Chapter 3. This homework exercise applies calculations and graphs.
1
A skydiver jumps from a plane at a great height and falls freely for a while. When approaching the
ground, the parachute is opened and the skydiver descends safely. The velocity–time graph for the
descent is shown in Figure 1.
Figure 1
a
b
Use data from Figure 1 to show that the initial acceleration of the skydiver is g (the value of
which is given in part 1c). Show your working clearly.
[4]
Look at the graph for the first 15 seconds. How does the graph indicate that air resistance is
acting, with increasing effect, on the skydiver?
[4]
c
Calculate the magnitude of the air resistance force acting on the skydiver at time t = 10 s. The
skydiver, together with the parachute pack, has a mass of 75 kg and g = 9.8 m s−2.
[4]
d
Explain in terms of forces why the graph is horizontal between about 15 and 65 seconds after
jumping, and find the distance the skydiver fell in this time.
[2]
e
The plane from which the skydiver jumped was at an altitude of 3.5 km. The parachute was
opened 65 s after the start of the skydive. Given that the skydiver fell 580 m in the first 15 s,
use the graph to find out how long the parachutist was in the air after the parachute opened.
(This time is actually before the end of the graph in Figure 1.)
Cambridge International AS and A Level Physics © Cambridge University Press 2014
[3]
1
2
Figure 2 is a distance–time graph for the first 90 s of this skydive, with the time axis labelled but
no scale on the distance axis, and no curve plotted.
Figure 2
Choosing a suitable scale for the y-axis, sketch the distance–time graph corresponding to the
velocity–time graph of Figure 1.
Cambridge International AS and A Level Physics © Cambridge University Press 2014
[3]
2