Answer:
screw and pulley
Explanation:
because they didn't have any of the other tools in that time
The reason why the snails are dead because the snails lack oxygen for it is a model of closed ecosystem. Another reason to this is that they lack abiotic factors that they need in surviving or as they live for the place that they are living lacks a lot and are not enough for them to last or survive. Lastly, the water could have not been a contributor for them to live for they may not be able to live in a water environment and could only dwell in land.
Answer:

Explanation:
The object is moving to and fro about its mean position
and the equation for its displacement is given as

now in one complete time period we know that the the object will complete its one oscillation
So the change in the position of the object in one complete time period will be ZERO
so here we can say that

since change in position is zero
so displacement = 0

During a climb UP the mountain, gravity does NO work on the climber.
Actually, it's more correct to say that gravity does NEGATIVE work
on him. The climber has to DO the positive work to haul himself up.
Work = (mass) x (gravity) x (height) .
For the guy in this problem:
Work = (67 kg) x (9.8 m/s²) x (3,500 meters)
= 2,298,100 joules.
If he eats no candy bars on the way, and completely depends on
his stored body fat for the energy, then he'll burn off
(2,298,100 joules) / (3.8 x 10⁷ joules/kg)
= 0.06 kg of fat.
That's only about 2.1 ounces. We KNOW he'll lose more weight than that,
climbing 11,000 feet. That's because climbing is pretty inefficient.
In addition to the potential energy you have to give your body weight,
you also have to expend energy breathing, digesting, metabolizing,
and sweating.
They exhibit identical behaviors with regard to changes of phase.
If there is any difference, it is too small to be measured, and none
has been observed.