C. Clear, dry weather. A good way to remember is H for high pressure = H for happy weather; L for low pressure = L for lousy weather (Glad I had someone to tell me this)
Time = 25s
speed = 10m/min
= 10m / 60
= (1/6)m/s
distance = speed × time
= 25 × (1/6)
=4.167m
The energy of a photon is given by

where

is the Planck constant
f is the frequency of the photon
In our problem, the frequency of the light is

therefore we can use the previous equation to calculate the energy of each photon of the green light emitted by the lamp:
Answer:
D) momentum of cannon + momentum of projectile= 0
Explanation:
The law of conservation of momentum states that the total momentum of an isolated system is constant.
In this case, the system cannon+projectile can be considered as isolated, because no external forces act on it (in fact, the surface is frictionless, so there is no friction acting on the cannon). Therefore, the total momentum of the two objects (cannon+projectile) must be equal before and after the firing:

But the initial momentum is zero, because at the beginning both the cannon and the projectile are at rest:

So the final momentum, which is sum of the momentum of the cannon and of the projectile, must also be zero:

Multiplied by; speed = distance x time