A hose directs a horizontal jet of water, moving with a velocity of 20m/s, on to a vertical wall. The
1 answer:
Force is defined as the rate of change of momentum.
The initial amount of momentum is
because water stops when it hit the wall total change of momentum must be 
.
Now let's calculate the force.
We need to find
. This is the amount of water hiting the wall per second.
Our final formula would be:
And now we can calculate the answer:
The initial amount of momentum is
Now let's calculate the force.
We need to find
Our final formula would be:
And now we can calculate the answer:
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a) the number of protons is more than the electrons
b)
Explanation:
The net electric charge on the ball is
This electric charge is given by the algebraic sum of the charge of the protons and of the charge of the electrons.
The charge of one proton is:
While the charge of one electron is
So the net charge on the metal ball will be given by
where
is the number of protons
is the number of electrons
So we find:
This means that the number of protons is more than the electrons.
b)
In this case, we want to make the ball neautral, so we have to remove a net charge of Q' such that the new charge is zero:
This implies that the charge that we must remove is
To do that (and to make the ball losing mass at the same time), we have to remove protons, since they have positive charge.
The number of protons that must be removed is:
The mass of one proton is
Therefore, the total mass that must be removed from the ball is
The first law of thermodynamics says that the variation of internal energy of a system is given by:
where Q is the heat delivered by the system, while W is the work done on the system.
We must be careful with the signs here. The sign convention generally used is:
Q positive = Q absorbed by the system
Q negative = Q delivered by the system
W positive = W done on the system
W negative = W done by the system
So, in our problem, the heat is negative because it is releaed by the system:
Q=-1275 J
while the work is positive because it is performed by the surrounding on the system:
W=+855 J
So, the variation of internal energy of the system is
where Q is the heat delivered by the system, while W is the work done on the system.
We must be careful with the signs here. The sign convention generally used is:
Q positive = Q absorbed by the system
Q negative = Q delivered by the system
W positive = W done on the system
W negative = W done by the system
So, in our problem, the heat is negative because it is releaed by the system:
Q=-1275 J
while the work is positive because it is performed by the surrounding on the system:
W=+855 J
So, the variation of internal energy of the system is