**Answer:**

50 lb

**Explanation:**

Given,

The weight of astronaut's life support backpack on Earth (w) = 300 lb

Acceleration due to gravity on Earth (g) = 9.8 m/s²

Acceleration due to gravity on Moon = g'

We know that weight of an object on Earth is,

Similarly, weight on Moon will be

Thus the astronaut's life support backpack will weigh 50 lb on Moon.

**Answer:**

defraction

**Explanation:**

when light passes from a less dense medium(air) into a dense medium(water) the light rays bend towards the normal. This makes the coin look closer

**Answer:**

**a)** 70 N, **b)** b. Each initially applied a force bigger than static friction to get the box moving and accelerating, then when the desired final speed was achieved they reduced the force to make the net force zero.

**Explanation:**

**a)** A constant speed means that magnitude of friction force is equal to the magnitude of the external force. The friction force is directly proportional to the normal force, which is equal to the weight of the box. Therefore, the magnitude of the force is 70 N.

b) Alice used initially a greater force to accelerate the box up to needed speed and later reduced the external force to keep speed constant. The right choice is option b.

**Answer:**

Addition of shells increases the distance of outer electrons from the nucleus.

**Explanation:**

Shielding effect is known as the attraction between the nucleus and an electron of any atom. In other words, it is the reduction in effective nuclear charge on an electron cloud.

Addition of electron shells results in the shielding of electron from nucleus. As the number of electron shells increases then farther will be the electrons placed from the nucleus and hence it will become easier to expel the electrons from outer shells with only little amount of ionization energy.

So, the amount of ionization energy require will be indirectly proportional to the shielding effect because more the shielding of electrons from the nucleus less will be the ionization energy require to expel the electrons.

**Answer:**

a

b

**Explanation:**

From the question we are told that

The mass of the ball is

The radius is

The speed is

The speed of the attached cord is

The position that is been considered is h

Generally according to the law of angular momentum conservation

Here is the initial momentum of the ball which is mathematically represented as

while

is the momentum of the ball at r = 2 ft which is mathematically represented as

So

=>

=>

Generally the resultant velocity of the ball is

=>

=>

Generally according to equation for principle of work and energy we have that

Here is the initial kinetic energy of the ball which is mathematically represented as

While is the sum of the total workdone by the ball

and is the final kinetic energy of the ball which is mathematically represented as

So

Here m is the mass which is mathematically represented as

here W is the weight in lb and g is the acceleration due to gravity which is

So

=>