Question

Shanda drives around a circular track exactly 12 times in 2 hours. Her speedometer constantly reads exactly 15 miles per hour during this time. Her average velocity is zero for the trip.
True or false

Answer 1

Im lost.... big time

Answer 2

Average velocity is defined as displacement over time.

Displacement is how far we move away from our starting point.

If we travel 100 miles in a big circle and end up back at our starting point we have a displacement of zero.

\[v_a = {0 \over 2 hrs}\]

This is because velocity is a vector quantity.

The driver's average speed, however, is not zero because this is a scaler quantity.

Answer 3

Ok! Can I ask you another??

Answer 4

Sure.

Answer 5

The force between your feet and the floor is greater while standing on your tiptoes than while standing flat on your feet.
True or False

False, right? Pressure equals force divided by area. Since the area decreases the pressure has to increase, but the force remains the same. The only way to increase the force is to gain weight i think.

Answer 6

Your intuition is right on! Good job!

Answer 7

:)) Yeah! Thanks I have one more that im clueless about....
Jane reads that passing a current of 100 milliamps through a person’s body from one hand to the other can be fatal. She accidentally grabs the positive terminal of her car’s battery in one hand and the negative in the other. Her car has a 12-volt battery rated for 100 amps. Jane would most likely be electrocuted by her careless action.
True or false.

Answer 8

The amperage rating of the batter doesn't matter. This is how many amps it is capable of outputting if it is short circuited.

Since the human body has some resistance, we can model this question as a circuit as shown.

The internal resistance of the human body is between 300-1000 Ohms (from here http://van.physics.illinois.edu/qa/listing.php?id=6793 ) While the skin has a resistance between 1000 - 10,000 Ohms.

Let's use worst case scenario of \[R = 100 \Omega + 1000 \Omega = 1100 \Omega\]

From Ohm's Law, \[I = {V \over R} = {12 \over 1100} = ??\]

Answer 9

So False, because Even with such a low resistance the current would only be 24 milliamps, which is not enough to kill?!?!?! :\

Answer 10

Well, thanks for all of your help!!!!!

Answer 11

That's correct!

Realize that if her resistance was higher, the current would be less. So 24 mA is the lowest value we would typically see.

Answer 12

Noted.