Answer:
angular velocity(ω) is the rate change of angular displacement.
ω=θ/t and it SI unit is rad/s
Explanation:
this is very similar with the definition of linear velocity (rate of change of displacement). it specifies the angular speed of an object and the axis about which the object is rotating.
Answer:

Explanation:
P = Power = 50 kW
n = Number of photons per second
h = Planck's constant = 
= Frequency = 781 kHz
r = Distance at which the photon intensity is i = 1 photon/m²
Power is given by

Photon intensity is given by

The distance is 
Answer: work must be done on the system (Option A)
Explanation:
The second law of thermodynamics is the fundamental law of nature; it states that energy can be transferred from cold objects to hot objects only, if work is done on the system. If energy is added to the system then as a result the thermal energy would increase. Second law of thermodynamics is used to determine whether a process is spontaneous or not. Moreover,the second law of thermodynamics is also used in refrigerators.
Answer:
because speed is the modulus of velocity which is a vector
the velocity to be zero it must be a round trip
Explanation:
This is because speed is the modulus of velocity which is a vector.
For the velocity to be zero it must be a round trip, therefore the resulting vector zero
On the other hand, the speed of the module is the same in both directions