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.
Answer:
the vertical acceleration of the case is 1.46 m/s
Explanation:
Given;
mass of the clarinet case, m = 3.07 kg
upward force applied by the man, F = 25.60 N
Apply Newton's second law of motion;
the upward force on the clarinet case = its weight acting downwards + downward force due to its downward accelaration
F = mg + m(-a)
the acceleration is negative due to downward motion from the top of the piano.
F = mg - ma
ma = mg - F

Therefore, the vertical acceleration of the case is 1.46 m/s²
Gravity increased the downward speed (or decreases the upward speed) by 9.8 m/s every second.
21.2/9.8 = 2.2 seconds
a yoyo in someones hand is an example of potential energy
Answer:
In a velocity selector, there are two forces namely;
» Electric field Intensity
» Magnetic field density
<u>Relationship</u><u>:</u>

E is the electric field intensity
B is the magnetic flux density