Physics chapter 4

When and if Galileo dropped two balls of the same size but different masses from the top of the Leaning Tower of Pisa, air resistance was not really negligible. Which ball actually struck the ground first. Why?

​-The heavier object hit the ground first because the terminal velocity was greater than the terminal velocity of the lighter object.

You exert a force on a ball when you toss it upward. How long does that force last after the ball leaves your hand?

​-the force exists on the ball until the ball is at its peak height where earth's gravity has brought it to a stop and the net force equals zero at that point

What happens to the weight reading on a scale you stand on when you toss a heavy object upward.

​-the reading on the spring scale will increase. When you toss the book up, the book pushes back down on you, by Newton's Third Law. So that means you push on the scale harder, so the reading on the scale increases.

In an orbiting space vehicle, you are handed two identical boxes, one filled with sand and the other filled with feathers. How can you determine which is which without opening the boxes?

If you try to push the boxes away from you and you have trouble, it will be the box with the sand in it because it has more mass and more interia than the box of feathers, because of friction.

Discuss whether or not a stick of dynamite contains force. In your discussion make the distinction betwen contain and exert

It exerts but but doesn't contain force

To pull a wagon across a lawn with constant velocity, you have to exert a steady force. Discuss and reconcile this fact with Newton's first law, which says that motion with constant velocity requires no force.

It has to be equal to friction. Net force=0, constant velocity

Upon which will air resistance be greater; a sheet of paper falling or the same sheet of paper wadded into a ball falling at a faster speed?

The falling sheet of paper will have more air resistance on it because it has less surface area than the wadded sheet so friction will not act as much on the wadded as the nonwadded one.

Consider a heavy crate resting on the bed of a flatbed truck. When the truck accelerates, the crate also accelerates and remains in place. Identify and discuss the force that accelerates the crate.

The friction force between the truck and the crate.

A crate remains at rest on a factory floor while you push on it with horizontal force F. What is the friction force exerted on the crate by the floor? Explain.

The friction force is equal to the horizontal force because they need to be equal to stay at rest.

When a junked car is crushed into a compact cube, does its mass change? It's weight? Explain.

The mass and weight should stay the same unless something would happen to fall off. The volume is being changed.

If a motorcycle moves with a constant velocity, can you conclude thta there is no ne force acting on it? How about if it's moving with constant acceleration?

The net for is 0 when it is at constant velocity. The accleration is proportional to the net force. Because F=ma

How does the terminal speed of a parachutist before opening a parachute compare to the terminal speed afterward? Why is there a difference?

The teminal speed of the parachutist with the parachute open is much lower than before; otherwise his speed would truly be "terminal". The reason is that the parachute has a much higher drag in air than the man alone, reducing the terminal velocity.

Sketch a path of a ball tossed vertically into the air. (Ignore air resistance) Draw the ball halfway to the top, at the top, and halfway down to its starting point. Draw a force vector on the ball in all three positions. Are the vectors the same or diffferent in three locations? Are the accelerations the same or different in the three locations?

Vectors are different because they're pointing in different directions. Accelerations are the same.

When you jump vertically off the ground, what is your acceleration when you reach your highest point? Discuss this in light of Newton's second law.

When you get to the highest point a=10m/s^2 and net force=0.

Which contains more apples; a 1lb bag of apples on Earth or 1 lb bag of apples on the moon? WHich contains more a 1kg bag of apples on the earth or a 1kg bag of apples on the moon?

a) 1lb bag of apples on the moon contains more apples because gravity on earth is much more than the gravitational pull on the moon. b) They both have the same number of apples because kg-mass so they have the same mass and number of apples

A 400 kg bear grasping a vertical tree slides down at constant velocity. What is the friction force that acts on the bear? Discuss how "constant velocity" is the key to your answer.

a=f/m. The friction force must be equal to the force exerted from the bear, to be constant velocity. a=9.8=net force/400 kg. Net force=3920N-friction force.

Aristotle claimed that the spped of falling object depends on its weight. We now know that objects in free fall, whatever the gravittaional forces on them, undergo the same gain in speed. Why don't differences in their gravitational forces affect their accleeration?

...

What is the net force acting on a 1kg ball in free fall?

10N

What is your own mass in kilograms? Your weight in newtons?

77.3kg, 48 N

What is the accleration of a rock at the top of its trajectory when it has been thrown straight upward? Is your answer consistent with Newtons second law?

Acceleration=9.8m/s^2

does mass of an astronaut change when he or she is visiting the international space station? Defend your answer.

No, because mass stays the same.

Why does a car that accidentally falls from the top of a 50 story building hit a safety net below no faster than if it fell from the 20th story?

Terminal velocity. By a certain height, terminal velocity kicks in and you reach a maximum. It happens very quickly.

When a coin is tossed upward, what happens to its velocity while ascending? It's acceleration? (ignore air resistance)

The acceleration is staying the same. Its velocity decreases

When your car moves along the highway at constant velocity, the net force on it is zero. WHy do you have to keep running your engine?

You have to have on the engine to remain at constant velocity because if it's shut off there is going to be friction causing the car to slow down.

When a car is moving in reverse, backing from a drive way, the driver applies the brakes. In what direction is the car's acceleration?

Forward

A race car travels along a raceway at a constant velocity of 200 km/h. What horizontal net force acts on the car?

0 because its going a constant velocity.

An astronaut drops an overhead rock on the Moon. Discuss what forces act on the rock as it drops

1.63 m/s^2 of gravity. Friction, also?

Boxes of various masses are on a friction-free, level table. Rank each of the following from greatest to least. a)net forces on the boxes. b)Accelerations of the boxes A. 5N<5kg>10N B. 10N<10kg>15N C. 10N<5kg>15N D. 5N<20kg>15 N

A) D, ABC B)AC, DB

A 100kg box of tools is in the lcations A, B, C. From greatest to least, rank the a)Masses of 100kg box of tools b) weights of the 100kg box of tools ...A-Earth, B-Moon, C-Jupiter

A) all are equal in mass B) C, B, A

A discussion partner says that, before the falling ball in the preceding exercise reachers terminal velocity, it gains speed while its acceleration decreases. Do you agree or disagree? Defend your answer.

As air resistance increases with increasing speed, accerlation and netforce will decrease.

How does the force of gravity on a raindrop compare with the air drag the drop encounters when it falls at constant velocity?

Because the drop is moving at constant velocity the net force acting on the raindrop is 0N. Therefore the force of gravity, say XN, pulling the drop downward is canceled out by the force of the air pressing onto the raindrop. So this force will be equal and opposite to the force of gravity, -XN.

A "shooting star" is usally a grain of sand from outer space that burns up and gives off light as it enters the atmosphere. What exactly causes this burning?

Fricition and a high velocity.

Make up two multiple choice questions that would check a classmates understanding of the disticition between mass and weight.

On the moon, which of these would change? a)your weight b)your mass c) both 2. Which of these is the unit of mass? a)lb b)kg c)N

In the absense of air resistance, if a ball is thrown verticlely upward with a certain inital speed, on returning to its original level it will have the same spped. When air resistance is a factor, will the ball be moving fast, the same, or more slowly than its throwing speed when it gets back to the same level? WHy>

The ball will fall slower because as it falls, the ball will gain speed until air resistance equals its weight. Then, acceleration will cease and the ball will fall at a constant speed (at terminal velocity).