Q3.14
It is spinning.
Q3.15
Gravitational potential energy is measured with respect to some reference height. Objects at lower height than that height will have negative potential energy.
Q3.16
Elastic potential energy is the kind of energy stored in stretched or compressed objects such as springs or rubber bands. I am sitting on a chair, with compressed springs and compressed foam, both of which have stored potential energy.
Q3.19
The work done by the engine has to equal the change in mechanical energy (kinetic plus potential) of the truck. The more kinetic energy the truck starts with, the less work it needs to do to make it ot the top.
P3.15
P3.24
P3.30
