# Warm-Up Exercise for lecture 20

## Due 8:00 am, Thurs, Nov 6

Physics 105, Fall 2008

Water flows from a pipe with large diameter into a pipe with smaller
diameter.
The pressure of the water in the small tube is

☐ greater than

☑ less than

☐ equal to

the pressure in the large tube

Water in a pipe is pumped from the ground (point A) through a narrow
constriction (point B) up to a second story apartment (point C). The pipe has
the same diameter at points A and C. How does the speed of the water compare at
the three points?

☐ A>B>C

☐ A<B<C

☑ A=C<B

☐ A=C>B

A ping pong player puts "topspin"
on the ball as he hits it to you by causing it to rotate such that the top of
the ball is spinning towards you. Where will the ball strike the table compared
to if it were not spinning?

☐ closer to you

☑ farther from you

☐ same distance

In the reading assignment for today, Ralph noticed two different
equations labeled "Bernoulli's Equation". One said, "*P*_{1} +
½ *r* *v*_{1}^{2}
+ *rgh*_{1} = *P*_{2}
+ ½ *r* *v*_{2}^{2}_{
}+* rgh*_{2}", the other said, "*P*
+ ½ *r* *v*^{2}
+ *rgh* = *C*". He wants to know how they can
both be the same equation when they look so different. What
can you tell him?

They both represent conservation of energy. The first says that energy is conserved between two points of a flow. The second says that the total energy is constant, regardless of which two points you choose.

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