Answer:
2.62seconds
Explanation:
Echo occurs when sound reflects and causing a delay before getting to the listener.
Let x be the distance from between the source and the reflector
t be the time taken for the echo to occur
v be the velocity of sound in air.
Using the relationship 2x = vt
t = 2x/v
Given x = 450metres
v = 343m/s
t = 2(450)/343
t = 900/343
t = 2.62seconds
It will take 2.62 seconds for him to hear his own voice echo off of the wall.
Answer:
Acoustic microstreaming
Explanation:
Acoustic microstreaming is the swirling effect produced by water stream confined in a spaced of a periodontal pocket.
- It is the movement of water in a particular direction as a result of mechanical pressure within the fluid body.
- They are often used in dental procedures to remove particulates from the teeth.
- It mostly relies on the properties of sound waves to achieve this goal
Answer:
Explanation:
Total heat gain by the block ΔQ = 2 x 12 kJ = 24 kJ .
Gain of potential energy = mgh = 12 x 9.8 x 32 = 3.763 kJ
Decrease in kinetic energy KE = 1/2 x 12 ( 40² - 7² )
= 9.306 kJ
increase in internal energy ΔE = 70 kJ
ΔQ = ΔE + PE - KE + W , W is work done by the gas
Putting the values
24 = 70 + 3.763 - 9.306 + W
W = - 40.457 kJ .
Since W is negative that means work is done on the system .
Another change that happened around the same time as discovery of fire was that their diets moved from nuts and berries to include meat. So, the correct option is (A)
<h3>What was the influence of Fire on Human Evolution?</h3>
Humans must have learned to handle fire very early in human history. Most likely due to natural sources such as lightning strikes and naturally occurring forest fires. It wasn't until much later that mankind invented how to make fire. Hominidae (genus Homo) appeared in East Africa about 2.5 million years ago, and fire is closely associated with many stages of evolution. The ability to cook food is thought to have led to the rise of Homo erectus from its more primitive ancestors.
Cooked foods provide much more energy than raw foods with low food consumption. This may have given time to develop social skills too. Cooked foods also detoxify potentially harmful bacteria. This has increased the variety of food available.
Cooking with fire is thought to have developed a large brain. These factors are thought to have driven the evolution of other human traits, including large brains and bodies, small teeth, modern limb proportions, and many social aspects of human-related behavior ( Wrangham et al. 1999). Indeed, by softening food, fire may have had a significant impact on extending human life beyond the age of healthy teeth.
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