Answer: 
Explanation:
Given
Distance between two speakers is 8 m
Man is standing 12 away from the wall
When the person moves 3 parallel to the wall
the parallel distances from the speaker become 4+3, 4-3
Now, the difference of distances from the speaker is

Condition for destructive interference is

for second destructive interference; n=2

I think it's true
I'm not really sure
Blue light can knock electrons off a plate, but red light can't
Answer:
15
Explanation:
P=W/T
T=6sec
W=?
F=60N
S=18m
W=F X S. .s indicate displacement
W=60x18
W=108
So p=108 j/6sec
P=15watt