We have switched to EJS 4 two months ago. There are many new features available and it also required larger jar file.
The typical size of EJS is 1.2-1.4M Byte if data analysis/video/translation... tools are all available (which is the current setting).
It will be slow if you have slow connection. It took 8-10 s to fullly load jar file for my browser.
You can remove some of the setting to reduce the file size to about 0.7-0.8M.

It took me 25-30 seconds to load your first page. The following is the error message when I load your second page:
[code]
Can not find Simple_pendulum_pkg.Simple_pendulumApplet.class?
java.lang.ClassNotFoundException: Simple_pendulum_pkg.Simple_pendulumApplet.class
at sun.plugin2.applet.Applet2ClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.plugin2.applet.Plugin2ClassLoader.loadCode(Unknown Source)
at sun.plugin2.applet.Plugin2Manager.createApplet(Unknown Source)
at sun.plugin2.applet.Plugin2ManagerAppletExecutionRunnable.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: java.io.IOException: open HTTP connection failed:http://downloadanswer.com/Documents/Simple_pendulum_pkg/Simple_pendulumApplet/class.class
at sun.plugin2.applet.Applet2ClassLoader.getBytes(Unknown Source)
at sun.plugin2.applet.Applet2ClassLoader.access000(Unknown Source)
at sun.plugin2.applet.Applet2ClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
... 7 more

[/code]

The jar tag in your applet is "Simple pendulum.jar" .

However, there is a space in your filename. Normally, I will create a file named as "Simple_pendulum".
Please reload your xml source "Simple pendulum.xml" , save it as "Simple_pendulum.xml" , compile it again and upload it to the server. This might solve your problem.
Please use only english alphabet ,number for your file name.  You can use underscore, but do not use " " (space) as part of file name.
Because EJS use your filename to name some of the class and variables.

I download your jar file and it is a corrupted jar. May be there are other problem!