Page 22 - Pra U STPM 2021 Penggal 1 - Physics

Physics Term 1 STPM Chapter 2 Kinematics

2

Figure 2.11
Info Physics
5. To slow down his fall, a skydiver spreads himself wide Highest free-fall
to increase the viscous drag (Figure 2.11). What happens October 14, 2012, Austria’s Felix Baumgartner
to the skydiver when his parachute opens? jumped off a helium-filled ballon at an altitude of
39,045 m and free-fall for 4 minutes, He reached
a speed of 1342.0 km h (1.24 times the speed
–1
of sound)
Example 9

A ball bearing is released from rest below the surface of a viscous liquid in a tall and wide container.
Sketch a graph to show how the height h of the ball bearing from the base of the container varies
with time. Explain the shape of the graph.
Solution:
z
If z = Instantaneous displacement from the liquid surface.
H = Height of liquid
z = H – h h = height from base of container
H
h = H – z
h
dh = – dz dH = 0
dt dt dt
= –v v = velocity of ball bearing

The initial velocity of the ball bearing is zero. Hence, when t = 0, gradient of graph = 0
The velocity of the ball bearing increases until the terminal velocity is achieved.
h

H

0 l

Since the gradient of h - t graph, dh = –v, the gradient becomes more negative until a constant
dt
negative value is obtained. When the terminal velocity is achieved, the h-t graph is straight.
Hence, the h-t graph is as shown.

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