The contact force is indeed caused by "Contact".
Air resistance is basically a type of friction, which is apparently present providing two object contact.
The rest selections are all interaction force, which is not necessarily caused by contact.
If both waves have the same wavelength, then the amplitude of
their sum could be anything between 1 cm and 9 cm, depending
on the phase angle between them.
If the waves have different wavelengths, then the resultant is a beat
with an amplitude of 9 cm.
Kinetic energy = (1/2) (mass) (speed²).
A Physicist in the canoe, or on a raft floating downriver next to the canoe, will say that the canoe's kinetic energy is zero.
A Physicist on the riverbank, watching the canoe drift by at 1 m/s, will say that its kinetic energy is 9 Joules.
They're both correct.
The sum is the result of adding 9260 and 3240 together. Each number can
be broken down into constituent parts in order to make addition easier.
Each place in the number represents its value, so a 2 in the hundreds
place represents 200.
You can separate numbers out this way to
make it easier to add them. 9260 can be broken down into 9000+200+60
while 3240 is 3000+200+40. You can then add these six numbers together.
60+40 = 100
200+200 = 400
9000+3000 = 12000
Then add your three partial results together to receive the final answer:
12000+400+100 = 12500
