Assuming there is not friction or air resistance, which of the following is true about total mechanical energy of a swinging pendulum?

It is the greatest at the top

It remains constant throughout the entire swing

It is zero the entire time

It is the greatest at the bottom

The answer is: It remains constant throughout the entire swing.

Explanation:

The "total mechanical energy" refers to the sum of the potential energy and the kinetic energy. When it comes to swinging pendulum, the total mechanical energy refers to the sum of the "gravitational potential energy" and the "kinetic energy."

Remember that the pendulum is "not in free fall" because it is constrained by a string. The tension in the string is being balance by a gravitational force that is acting on it. So, when the pendulum swings (back and forth), the gravitational potential energy and the kinetic energy undergoes a constant exchange of energy. So, this allows the mechanical energy to be conserved.

If friction is present, the mechanical energy will then be turned into other forms of energy.

as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2