exercises on chapter 12-14

Ch 14. 4: if you count the tires on a large tractor-trailer that is unloading food at your local super market, you maybe surprised to count 18 tires. why so many tires?

The huge weight of the truck and its contents are spread over a larger surface area, decreasing the pressure on each tire so it does not destroy the road surface.

Ch 14. 24: on a sensitive balance weigh an empty, flat, thin plastic bag. Then weigh the bag filled with air. With the readings differ?

No, provided the air is not compressed. The bag with air in it weighs more, but it also has buoyant force that equals the weight of the air inside.

Ch 12. 18: when you bend meterstick, one side is under tension and the other is under compression. which side is which?

The concave (bottom) side is under compression, the convex (upper) side is under tension

Ch 12. 6: what happens to the density of air in a common rubber balloon when it is heated?

The density decreases as the volume of the balloon increases

Ch 14. 8: How does the density of air in a deep mine , compare with the air density of air at the earths surface?

The density of air in a deep mine is greater than the surface because there is a greater quantity and weight of air pushing down on you

Ch 12. 22: the sketches are of top views of a dam to hold back a lake. which of the two designs is preferable? why?

The design where the dam curves into the water because the weight of the water compresses the dam, forcing the parts of the dam together like an arch, making it even stronger

Ch 13. 16: a block of aluminum with a weight of 10 N is placed in a beaker of water filled to the brim. water over flows. the same is done in another beaker with a 10N block of lead, does the lead displace more, less or the same amount of water?

A 10N block of Al is much larger than a 10N block of Pb

Ch 13. 4: which do you suppose exerts more pressure on the ground-a 500kg elephant or 50 kg land standing on spike heels?

A lady in spike heels will exert 10 times the pressure than an elephant foo

Ch 13. 2: you know that a sharp knife cuts better than dull knife. do you know why this is so? defend your answer

A sharp knife; it has a thinner cutting area which results in more cutting pressure

Ch 12. 12: which has more volume, a kilogram of gold or a kilogram of aluminum?

Aluminum has more volume because it is less dense

Ch 14. 26: The little girl sits in a car at a traffic light holding a helium filled ballon. the windows are closed and the car is relatively airtight. When the light turns green and the car accelerates forward, her head pitches backward but the ballon pitches forward . Explain why.

As the car accelerates, the air moves toward the rear of the car, causing the air at the front to be momentarily less dense; the balloon will always move to an area of decreased density and it will always move in the direction of acceleration.

Ch 14. 6: why is a soft, under inflated football at sea level much firmer when it is taken to a high elevation in the mountains?

At higher altitude, less atmospheric pressure is exerted on the ball's exterior, making relative pressure within greater, resulting in a firmer ball

Ch 12. 24: why do you suppose that girders are so often arranged to form triangles in the construction of bridges and other structures?

Because a triangle is the most rigid of geometrical structures. A rectangular shape is very easy to distort

Ch 13. 26: why will a block of iron float in mercury but sink in water?

Because mercury has a high density, Fe can displace its own weight and float in the mercury; It cannot displace its own weight in water because water is much less dense.

Ch 12. 26: only with great difficulty can you crush an egg when squeezing it along its long axis, but it breaks easily if you squeeze it sideways. Why?

Because the ends of an egg form arches and pressing them together just strengthens the egg; the sides do not form a catenary shape and will easily crack.

Ch 13. 22: suppose that you wish to lay a level foundation for a home on hilly and bushy terrain. how can you use a garden hose filled with water to determined equal elevation of distant points?

Because the levels at each end of a clear hose will always be the same, regardless of the terrain between them.

Ch 14. 2: Why is there no atmosphere on the moon?

Because the speed of gas molecules on the surface exceeds the lunar escape velocity due to the smaller gravitational force of the moon.

Ch 13. 14: a block of aluminum with a volume of 10 cm3 is placed in a beaker of water filled to the brim. water overflows the same is done in an other beaker with 10cm3 cube block of lead. does the lead displace more, less or the same amount of water.

Both blocks have the same volume and will displace the same amount of water

Ch 13. 6: the photo shows physics instructor marshal Ellenstaian walking barefoot on broken class, bottle in this class. What physics concept is he demonstrating, and why is he careful that they broken pieces are small and numerous?

By having many small pieces of glass his weight is applied over a large surface area; the sharp glass will not have enough pressure to cut his feet.

Ch 14. 36: You and tim float a long string of closely spaced helium balloons over his used-car lot. You secure the two ends of the long string of balloons to different points on the ground so that the balloons flat over the lot in an arch. What is the name of the arch?

In the shape of a catenary.

Ch 13. 18: their is a legend of a dutch boy who bravely held back the hole north sea by plugging a hole in a dike with his finger, is this positive or reasonable?

It is reasonable because the force on his finger will be very small as the pressure of the water will be due to the distance of the leak below sea level

Ch 13. 10: If water faucets upstair and downstair are turned fully on, will more water per second flow out of the up stair faucets or the down stair faucets?

More water from the downstairs faucets; the bottom faucets are "deeper" than the upstairs, so the pressure is greater

Ch 14. 14: The "pump" in a vacuum cleaner is merely a high-speed fan. would a vacuum cleaner pick up dust from a rug on the moon? explain.

No, it wouldn't work because it requires atmospheric pressure to push the air into the lower pressure chamber in the vacuum and the moon has no atmosphere.

Ch 14. 38: Two identical balloons of the same volume are pulled up with the air to more than atmospheric pressure and suspended on the ends of a stick that is horizontally balanced. One of the balloons is the punctured. is the balance of the stick upset? If so what way does it tip?

The side with the punctured balloon will tip upwards since it contained air at a higher density of the air around it and that side of the stick now weighs less.

Ch 13.8: Why does your body get more rest when your lying down than when your sitting? is blood pressure I'm your leg greater?

Your body gets more rest when you are lying down because the heart does not have to pump blood to sitting or standing heights