A vertical rectangular wall with a width of 20 m and a height of 12 m is holding a 7-m-deep water body. The resultant hydrostatic force acting on this wall is (a) 1370 kN (b) 4807 kN (c) 8240 kN (d) 9740 kN (e) 11,670 kN

(c) 8240 kN

Resultant hydrostatic force F = 8240 kN

Explanation:

Force can be expressed as;

F = ma

F = mg 1

Where,

F = force

m = mass

a = acceleration

g = acceleration due to gravity

And we know that mass of an object is the product of

Density and Volume

m = pV

And volume V = area × height = Ah

m = pAh 2

Substituting m into equation 1

F = pAhg = pghA 3

Given;

Density of water p = 1000kg/m^3

g = 9.81m/s^2

Area A = 20m × 12m = 240m^2

h = depth/2 = 7/2 = 3.5m

Substituting the values into equation 3, we have;

F = 1000×9.81×3.5×240

F = 8240400 N

Resultant hydrostatic force F = 8240 kN

a.   mass number from atomic number

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.