Help please? I dont understand what this means.

At present most of the world's energy needs are supplied by what kind of energy

antiseptic1488 [7]

Fossil fuels . . . coal, oil, natural gas

Among primitive cultures, wood is an important source.

4 0

3 years ago

Light travels in a straight line at a constant speed of 300 000 km/s what is the lights acceleration

exis [7]

Answer:

it's acceleration is 0

Explanation:

since it is travelling at a constant speed it is not accelerating so its acceleration is 0

3 0

3 years ago

Use Snell's Law to solve the following:

azamat

Answer:

1.171

Explanation:

if n₁sinΘ₁=n₂sinΘ₂, then n₂=n₁sinΘ₁ / sinΘ₂;

$n_2=\frac{1.5*sin45}{sin65}=\frac{1.5*0.707}{0.906} =1.1705$

3 0

3 years ago

A 12.8-kg monkey hangs from a cord suspended from the ceiling of an elevator. The cord can withstand a tension of 156N and break

Varvara68 [4.7K]

Answer:

$2.4 m/s^2$

Downward

Explanation:

We are given that

Mass of monkey=12.8 kg

Tension=156 N

We have to find the magnitude of the elevator's minimum acceleration.

$T=m(g+a)$

Where $g=9.8 m/s^2$

Substitute the values

$156=12.8(a+9.8)$

$9.8+a=\frac{156}{12.8}=12.2$

$a=12.2-9.8=2.4 m/s^2$

Hence, the acceleration = $a=2.4 m/s^2$

Direction of the elevator's minimum acceleration is downward because the elevator moves downwards.

8 0

3 years ago

Suppose that an asteroid traveling straight toward the center of the earth were to collide with our planet at the equator and bu

vlada-n [284]

Answer:

$\frac{1}{10}$ M

Explanation:

To apply the concept of angular momentum conservation, there should be no external torque before and after

As the asteroid is travelling directly towards the center of the Earth, after impact ,it does not impose any torque on earth's rotation, So angular momentum of earth is conserved

⇒ $I_{1} \times W_{1} =I_{2} \times W_{2}$

$I_{1}$ is the moment of interia of earth before impact
$W_{1}$ is the angular velocity of earth about an axis passing through the center of earth before impact
$I_{2}$ is moment of interia of earth and asteroid system
$W_{2}$ is the angular velocity of earth and asteroid system about the same axis

let $W_{1}=W$

since $\text{Time period of rotation}∝$ $\frac{1}{\text{Angular velocity}}$

⇒ if time period is to increase by 25%, which is $\frac{5}{4}$ times, the angular velocity decreases 25% which is $\frac{4}{5}$ times

therefore $W_{1}$ $=$ $\frac{4}{5} \times W_{1}$

$I_{1}=\frac{2}{5} \times M\times R^{2}$ (moment of inertia of solid sphere)

where M is mass of earth

R is radius of earth

$I_{2}=\frac{2}{5} \times M\times R^{2}+M_{1}\times R^{2}$

(As given asteroid is very small compared to earth, we assume it be a particle compared to earth, therefore by parallel axis theorem we find its moment of inertia with respect to axis)

where $M_{1}$ is mass of asteroid