Alkali metals alkaline earth metals and halogens and noble gases. I’m pretty sure
If the echo (the reflected sound) reaches your ear less than about
0.1 second after the original sound, your brain doesn't separate them,
and you're not aware of the echo even though it's there.
If the echo comes from, say, a wall, 0.1 second means you'd have to be
about 17 meters away from the wall. If you're closer than that, then the
echo reaches you in less than 0.1 second and you're not aware of it.
A. 30 meters . . .
No. You hear that echo easily
B. you're standing within range of both sounds . . .
No. You hear that echo easily, if you're at least 17 meters from the wall.
C. less than 0.1 second later . . .
That's it. The echo is there but your brain doesn't know it.
D. 21.5 meters
No. You hear that echo easily.
The mass of a radioactive element at time t is given by
where
is the mass at time zero, while
is the half-life of the element.
In our problem,
, t=121.0 s and
, so we can find the initial mass
:
C
Unbalanced causes something to move because the net force is greater than zero
Answer:
a2 = 2.5 m/s2
Explanation:
F1 = m1 a1 We use the same force so F1 = F2
= 5kg × 15m/s2 F2 = m2 a2
= 75N a2 is required
a2 = F2 / m2
= 75N / 30 kg
= 2.5 m/s2
