Physics 10C Midterm

Some climatologists say that our climate could be warm enough to melt the polar ice caps, sending the resulting water down towards the equator. If this were to happen, the length of the day would

Increase due to angular momentum conservation.

What will cause a person to slide down a slope faster?

Increase the degree of the slope With weight or no weight?

If the net work done on an object is positive, then the object's kinetic energy

Increases

If you put a scale on an incline, what will your weight be compared to when it is flat?

It is less because only a portion of the downforce vector is measured.

How does adding salt to water affect boiling rate?

It slows down the boiling rate because salt increases the boiling point. With an increased temperature to boil, the reaction is slower.

In making ice cream, the flavored cream is in a container in contact with melting ice. When the ice cream freezes it give energy up to the ice / water mixture. What happens to the temperature of the ice / water mixture?

It will not change because the energy is going into its melting the ice.

Consider two skiers Julia and Ted with masses m1 and m2 at the top of the mountain. Both start from rest at the same height. However, Ted takes a less difficult slope with 30 degree angle with the horizontal, while Julia takes steeper slope with 45 degree angle (those are called black diamond runs). Which skier will reach the bottom of the hill faster?

Julia

Compare the kinetic energy of a 20,000-kg truck moving at 110 km/h with that of an 80.0-kg astronaut in orbit moving at 27,500 km/h.

Kinetic energy of the truck is smaller than the kinetic energy of the astronaut

Consider two skiers Julia and Lindsay with masses m1 and m2 at the top of the mountain. Lindsay weighs more than Julia. Both start from rest at the same height and take th same slope down the hill. At the bottom of the hill (ignore air resistance; mark all correct answers)

Lindsey's kinetic energy will be higher but they will have the same speed.

5.5 grams of salt added to 0.5 liter of water. The freezing point of this solution is _____ pure water.

Lower than

There are 100 Calories (1Cal= 4200J) of energy in a cnady bar. Calculate how many stairs you can climb with just one candy bar. Assume a stair is 25cm in height. Use actual mass.

PE= m*g*h 100*(4200J/1Cal) = 420,000J 420,000J= 58kg*9.8m/s/s*h h=739 739m/0.25m=2956 steps

If you eat a candy bar with 420,000J of energy and slide down a hill, what will be your final velocity? Use your mass.

PE=mv^2 420,000J=58kgv^2 v=120m/s

What are the boiling and freezing points of saltwater?

Saltwater boiling is higher than freshwater. Saltwater freezing is lower than freshwater.

When sitting still on the ground, a tricycle is in a state of

Static stable equilibrium

In studying many martial arts, it is necessary to practice efficient and safe postures. One important concept related to how one should stand is that the feet should be reasonably far apart, because

The base of support is wider, thus stabilizing the person

What will happen when a boulder is rolled off a hill?

The boulder will stop at a point lower than where it started.

Skis and snowboards should not slide on snow because the friction between snow and ski base is too high. You have seen though that they slide pretty well. Why?

The friction is smaller due a layer of water that forms in between.

A woodpecker is pecking on a tree. it reaches max. speeds of 7 m/s and decelerates in 0.0005. What is the head's deceleration and what is this in "g's"?

The head goes from 7 to 0 and since it is decelerating the difference will be -7. It decelerates at a rate of (-7m/s)/(0.0005s)=-14,000 m/s/s In g's this is (14,000m/s/s)/ 10m/s/s= 1400x greater in gravitational acceleration.

What is the normal force for a person standing on a flat surface vs on a slope?

The normal force is is perpendicular to the surface the person is standing on. The normal force length decreases as the slope increases.

You go to a quick - fix garage to get your brakes worked on. When your tires are re-installed, the mechanic forgets to put the lug nuts on your tires. Although nobody gets hurt, a tire comes off your car when you are traveling fairly rapidly and it is able to roll through a very large distance, even hitting bumps and objects in the way. Please explain why the tire can roll so far without tipping over.

The tire becomes a gyroscope and therefore enjoys dynamic stability.

A truck weighs twice as much as a car, and is moving at twice the speed of the car. Which statement is true about the truck's kinetic energy compared to that of the car?

The truck has 8 times the kinetic energy of the car.

You get a job as a dish washer to help with your college bills. The first thing the management tells you is to be very careful of the steam - it is exceedingly dangerous. In fact, steam at 100C can burn you much more than water at 100C.

The two substances are at the same temperature, but steam has more energy than the same mass of water, it takes energy to vaporize liquid.

Suppose an ice skater is moving on the surface of a frozen lake at constant velocity. What is true about the external (outside) forces acting on the skater?

There could be some but they all cancel out.

Where is gravitational pull when a person stands on a flat surface vs on a slope?

They both have equal gravitational pull that goes straight down.

How is the direction of angular momentum determined?

Use the right hand rule and follow the roll of the fist.

How does altitude affect boiling rate?

When pressure increases, BP increases. This means that at a lower elevation the BP is higher than at a higher elevation where there is less pressure.

Suppose Larissa throws a ball up in the air and it comes back down to the same place she threw it from. Ignoring times when the ball is in contact with her hand, and ignoring air resistance (friction with the air), identify the point where the ball has equal kinetic and potential energy:

When the ball is halfway between Larissa's hand and the highest point

Suppose Larissa throws a ball up in the air and it comes back down to the same place she threw it from. Ignoring times when the ball is in contact with her hand, and ignoring air resistance (friction with the air), identify the point where the ball has maximum potential energy:

When the ball is highest in the air.

You are riding a multi-speed bicycle up a steep hill that's 100 m high and want to do as little force as possible on your way up the hill.

You should choose the smallest crank sprocket (attached to the pedals) and the largest freewheel sprocket (attached to the rear wheel).

You are riding a multi-speed bicycle up a steep hill that's 100 m high and want to do as little work as possible on your way up the hill (remember the definition of work)

Your choice of gears doesn't matter because you'll do the same amount of work climbing the hill no matter which gear you choose.

What is the formula for centripetal acceleration?

a(sub c)= v^2/r

What is the resulting force when a person is: a) standing on a flat surface? b) standing at a 25 degree angle? c) standing at a 45 degree angle?

a) normal and gravitational forces are equal and opposite b) gravitational force is stronger than normal force c) gravitational force is even stronger than normal force

What are the boiling and freezing points of freshwater?

boiling: 100 degrees C (212F) melting: 0 degrees C (32F)

What is kinetic energy?

energy of motion that is converted from potential energy.

If a body doesn't change its position with respect to it's surroundings then it's in state of

equilibrium

You are cooking dinner in Tahoe for your friends after skiing. The pasta you are making will take ____ to cook as compared to Davis.

longer than

You drive to Tahoe. The boiling point of water is _____ than in Davis.

lower than

Melting is a _______ ______ that requires energy ________ for the melting system.

phase transition, input

You can balance a broom on your hand if you're careful. To do this trick well, you must look at

the middle of the broom

It is important for cyclists to lean their bicycles while negotiating sharp turns because

the torque created by their leaning balances out the frictional torque from the road which would tend to flip them.

Why do we add salt to the ice?

to decrease the freezing point of water

When trying to track-stand (stand still, without putting your feet on the ground) on a bicycle, a bicycle is in a state of:

unstable static equilibrium

Is it possible to ride a backwards bike from MU to Roessler 55 (one where wheel goes to the left when you turn it right)?

yes

An ice skater performs a pirouette by pulling in his outstretched arms close to his body thereby decreasing the moment of inertia (i.e. rotational mass) to 0.6 times its initial value. The angular velocity of the skater will be.

1.7 times the initial value

Land west of the San Andreas fault in southern California is moving at an average velocity of about 6 cm (0.06 meters) per year northwest relative to land east of the fault. Los Angeles may thus someday be at the same latitude as San Francisco. How far in the future will this occur if the displacement to be made is 590 km (590,000 meters) northwest, assuming the motion remains constant?

10 million years

A snowboarder in a frictionless half pipe is doing tricks. He weighs 100kg and jumps 10m high. What is his potential energy (assume g=10m/s^2)?

10,000J

Suppose the ski patrol lowers a rescue sled and victim over the overhanging cliff, having a total mass of 90.0 kg, down a 30 m cliff? What is the total work done?

27000J

Which formula is used to find the speed of a bike at the bottom of a hill given the mass of the rider, the height of the hill, and the rotational mass.

2mgh=mv^2 + Iv^2/r^2

There are 100 Calories (1Cal = 4200J) of energy in a candy bar. If the snowboarder eats one of those and would be able to convert all the energy into jumps (without making extra tricks, assume all he needs is just the total energy needed for to lift him to the maximum height), how many times (approximately) would he be able to run the course and jump to 10m high?

40

How are 6 sided snowflakes formed?

6 sided angles are formed by oxygen and hydrogen bonds

Suppose you are riding on a merry - go - round and you move out to the edge. Why does the rotational rate of the system decrease?

Angular momentum is conserved and the moment of inertia increased.

Suppose you go from the earth to a planet where the acceleration of gravity is half that of the Earth. On the new planet your weight will be about

Be half its value on earth.

What is heat?

Energy that is transferred when two systems have different temperatures. Energy goes from high to low temperature.

Which of the following best explains why sweating is important to humans in maintaining suitable body temperature?

Evaporation of moisture from the skin extracts heat from the body.

For momentum to be conserved in a system it must:

Experience no net external force.

Avalanches occur due to:

Gravity

Why does an ice cube feel cold?

Heat from your hand enters the cube by conduction.

If the earth's rotational mass increases or decreases by (5*10^-9) from its initial mass of 1, what will the effect on day length be?

I(1)*W(1)=I(2)*W(2) 1*(1 rotation/86,400s)=(1+5*10^-9)*W(2) W=0.00347 1*(1 rotation/86,400s)=(1-5*10^-9)*W(2) W=0.00340

Remember that angular momentum is conserved. angular momentum=rotational mass* angular velocity. If rotational mass decreases 50% what happens to angular velocity?

I(1)*W(1)=I(2)*W(2) I(1)/I(2)= W(2)/W(1) when one increases, the other decreases in a proportional relationship.

Suppose Larissa throws a ball up in the air and it comes back down to the same place she threw it from. Ignoring times when the ball is in contact with her hand, and ignoring air resistance (friction with the air), identify the point where the ball has maximum kinetic energy:

-When it leaves Larissa's hand and when it falls back into Larissa's hand.

A bike wheel rotates through 2 revolutions in 4 seconds. What is the linear sped of a point 0.50m from the center of the wheel?

1 revolution in 2 sec so half a revolution in 1 sec. Pi/revolution 3.14*0.5m= 1.57m/s

What 3 things help keep a bike upright?

1) the center of mass is in front of the steering axis 2) the front wheel hits the ground behind the steering axis 3) gyroscopic effect of the wheel