Physics Midterm
12. The force will be the same on the two vehicles, according to Newton's Third Law. That means the sports car, with far less mass, will experience a much greater acceleration, according to Newton's Second Law.
If a massive truck and small sports car have a head-on collision, upon which vehicle is the collision force greater? Which vehicle experinces the greater acceleration?
19. Is the sports car will experience the greater force. The 18-wheeler tractor will have a greater impulse and momentum. The sports car will experience the greater acceleration. force same for both.
If an 18-wheeler tractor-trailer and a sports car have a head-on collision, which vehicle will experience the greater force of impact? The greater impulse? The greater change in momentum? The greater acceleration?
4. The same power when both are raised in the same time; Twice the power for the lighter sack raised in half the time.
If both sacks in the preceding question are lifted their respective distances in the same time, how does the power required for each compare? how about for teh case where the lighter sakc is lifted its distance in half the time?
9. The mass of the cannon is more, so it has more inertia.
If the forces that act on a cannonball and the recoiling cannon from which it is fired are equal in magnitude, why do the cannonball and cannon have very different accelerations?
5. Assuming that the water is sourced from "downstairs" (or below) and the pipes and faucets are all of the same dimensions, the lower level faucet will produce more water for two reasons:
If water faucets upstairs and downstairs are turned fully on, will more water per second flow out of the donwstairs faucet? Or will the water flowing from the faucets be the same?
1. force x distance but power = work done/time which equates to power= force x velocity. So basically, you would have to have applied the same force for the work to be equal so therefore it is your velocity that is different.
If you ran up the stairs in half the time of another person of equal weight, you did the same work but used twice the power. Explain.
It will land in your hand. It will land in front of you. If the train makes a turn while the coin is in the air, it will land off to the side of you.
If you toss a coin straight upward while riding in a train, where does the coin land when the motionn of the train is uniform along a straight-line track? When the traisn slows while the coin is in teh air? When the train is turning?
50 km/h. The coin is moving with the same inertia as the bus.
If you're in a smooth-riding bus that is going at 50 km/h and you flip a coin vertically, what is the horizontal velocity of the coin in midair?
2. Mass is the same, so if the whale is taking up less volume, the density must have increased. The whale has displaced a greater mass of water at the depth, so the buoyant force is greater.
In a deep dive, a whale is appreciably compressed by the pressure of the surrounding water. What happens to the whale's density?
15. Both astronauts will move due to Newton's 3rd law. Since Ken is pulling Joanne towards him, the rope will react and pull him towards Joanne.
In a tug-of-war between two physics types, each pulls on the rope with a force of 250 N. What is the tension in the rope? If both remain motionless, what horizontal force does each exert agains teh ground.
6. a) a = v/t = 9m/s/0.2s = 45m/s squared
Leroy, who has a mass of 100 kg, is skateboarding at 9.0 ms when he smacks into a brick wall and comes to a dead stop in 0.2 seconds (A) show that his decelration is 45 m/s^2
19. Momentum is completely transferred from car A to car B. Since the masses are the same, the speed of car B is equal to the initial speed of car A.
Railroad car A rolls at a certain speed and makes a perfectly elastic collision with car B of the same mass. After the collision, car A is observed to be at rest. How deso the speed of car B compare wit the initial speed of car A?
10. Weight W = mg; where m is the mass of an object and g is the acceleration (in a vacuum) of the object and due to the force of gravity, its weight. That is g = W/m where the force of gravity is acting on the body of mass m. Gravity causes weight, but it is not the weight.
What do we call the gravitational force between the Earth and your body?
16. Same weights and same pressures.
What happens to the pressure in all parts of a confined flued when the pressure in on epart is increased?
19. When an object has reached it's terminal velocity it's acceleration is zero.
What is the acceleration of a falling object when it reaches its terminal velocty.
It's is the equilibrium rule. The ∑ stands for "vector sum", F stands for "forces".
What is the meaning of ∑F=0
1. The net force is 0.
What is the net force on a bright red Mercedes convertible travling along a straight road at a steady speed of 100 km/h?
Average Speed= 50/10 Average Speed= 5 1 minute= 60 seconds At the same average I'd go six times as far in six times the time. In one minute I'd travel 6 x 50= 300.
What is your average speed if you run 50 m in 10 s? Show that the distance you'd travel at this speed for 1 minute would be 300 m
5. 105 lbs= 467.06 N work= 467.06x15 m 7005.9 j power=7005.9j/180s 38.92 horsepower
What was your calculated horsepower? Show your work.
When you pulled the card board slowly,the coin will join the card board but when you quickly withdraw the cardboard the coin shot unto the glass.Newton's first law of motion states that if an object will stay at rest, it will remain at rest.
When the card was pulled slowly, the coin moved with it, but when the card was flicked (moved quickly), the coin dropped in the glass. Explain.
1. The truck at rest has no speed, hence no momentum. So the moving automobile has greater momentum.
Which has greater momentum, a heavy truck at rest or a moving automobile?
16. The most important part of winning a tug-of-war battle is pushing harder on the floor.
Which is most important in winning a tug-of-war-pulling harder on the rope, or pushing harder on the floor?
3. It is the same, for the product of each is the same; (50 kg)(2 m) = (25 kg)(4 m).
Which requires more work—lifting a 50-kg sack a vertical distance of 2 m or lifting a 25-kg sack a vertical distance of 4 m?
12. Stopping and then reversing direction is a greater change in momentum and therefore requires a greater impulse.
Which requires the greater impulse, stopping something dead in its tracks or stopping it and then reversing its direction?
3. Also, as f=ma (Newtons 2nd law), if both may achieve the same acceleration the one with the greater mass (the heavier) has the advantage.
Who has the greatest advantage of having the most horsepower: someone who is light and quick or someone who is heavy and quick? Explain.
The law of inertia applies in both cases. When the bus slows, you tend to keep moving at the previous speed and lurch forward. When the bus picks up speed, you tend to keep moving at the previous (lower) speed and you lurch backward. Newton's Third Law of Motion : To every force there is an opposite and equal force.
Why do you lurch forward in a bus that suddenly slow? Why do you lurch backward when it picks up speed? What law applies here?
5. There is greater pressure against the bottom.
Why does buoyant force act upward on an object submerged in water?
3. Impulse equals a change in momentum, not momentum itself.
Why is it incorrect to say that impulse equals momentum?
7. The time to come to a stop will be longer on the mat. This means a longer time to stop and a smaller force.
Why is it less damaging if you fall on a mat than if you fall on a solid floor?
14. It has vertical and horizontal components. The vertical relates to how high the ball will go. The horizontal components relates to horizontal range of the ball. Wt=mg
With no air drag, what happens to the horizontal component of velocity for the batted baseball?
7. The two scales on different parts of the same rope have to have the same reading because the rope is experiencing tension as a whole everywhere, and it will be the same wherever you measure it.
Your teacher challenges you and your best friend to pull on a pair of scales attached to the ends of a horizontal rope, in tug-of war fashion. Can you each pull in such a way that the readings on the scales will differ.
2. The reason that a heavy body doesn't fall faster than a light body is because the greater gravitational force on the heavier body (its weight), acts on a correspondingly greater mass (inertia). The ratio of gravitational force to mass is the same for every body—hence all bodies in free fall accelerate equally. And it's true not just near the Earth, but anywhere.
Gravitational force acts on all bodies in proportion to their masses. Why doesn't a heavy body fall faster then a light body?
It depends on perception. Let's say I'm on a train and I'm sitting down. From my perspective I'm at rest, I'm really not doing anything. But, a person standing on the platform watching my train go by will think I'm moving fast, because the train is moving. When only a pair of equal and opposite forces act on an object the net force is zero.
How can you be both at rest and also moving at 100,000 km/h at the same time?
17. The blades push down on the air, and the air pushes back up on the blades.
How does a helicopter get its lifting force?
7. A submerged object displaces a volume of water equal to the object's volume
How does the buoyant force on a fully submerged object compare with the weight of water displaced?
13. Both are the same.
How does the downward pressure of the 76-cm column of mercury ina barometer compare with the air pressure at the surface of teh dish of mercury that it stands in?
16. When anything falls at constant velocity, air drag and gravitational force are equal in magnitude. Raindrops are merely one example.
How does the force of gravity on a raindrop compare with the air drag it encounteres when it falls at constant velocity?
2. There is more pressure the deeper you go.
How does the pressure exerted by a liquid change with depth in the liquid? How does the pressure exerted by a liquid change as the density of the liquid changes?
6. The volume of space that would have been occupied by water is now occupied by the object. In other words, the displacement is equal in volume to that which has caused the displacement.
How does the volume of a fully submerged object compare with the volume of water displaced?
1. W = 2 J
How many joules of work are done when a force of 1 N moves a book 2m?
6. Energy = Force x distance the force is applied through = (1N)(2m) = 2J. Power = Change in Energy / time elapsed = 2J / 1s = 2W.
How many watts of power are pended when a force of 1 N moves a book 2 m in a time interval of 1 s?
1. 10kg(-6 m/s)= -60 kg m/s= 60 kg m/s backward
How much impulse is needed to stop a 10-kg bowling bowling ball moving at 6 m/s?
14. Increasing force means decreasing distance, so the distance moved by four fold force is one fourth as much
If a machine multiplies force by a factor of 4, wha other quantity is diminished, and by how much?
30 N- 20 N= 10 N
(B) Both forces act in opposite directions.
b)F = ma = 100kg x 45m/s squared = 4500N
(B) Show that the force of impact is 4500 N
7. Momentum before = momentum after (5kg)(1m/s) + (1kg)v = 0 5m/s + v = 0 v = -5 m/s So if the little fish approaches the big fish at 5 m/s, the momentum after will be zero.
A 5-kg fish swimming 1 m/s swallows an absentminded 1-kg fish swimming toward it as a speed that brings both fish to a halt immediately after lunch. Show that the speed of the approaching smaller fish before lunch must have been 5 m/s.
2. Water pressure will be higher downstairs due to gravity
A 6-kg piece of metal displaces 1 L of water when submerged. Show that its density if 6000 kg/m^2. How does this compare with the desntiy of water?
2. In accords with the inverse-square law, four times as far from the Earth's center diminishes the value of g to g/42, or g/16, or 0.6 m/s2.
Find the change in the force of gravity between two planets when the masses of both planets are doubled but the distance between them stays the same.
9. Ep = 1x9.8x4 = J Ep = 1x9.8x8 = J
How many joules of potential energy does a 1-N book gain when it's elevated 4 m? When it's elevated 8 m?
5. PE = mgh = 1.5 x 10 x 2 = 30 J PE = 1.5 x 10 x 4 = 60 J
How many joules of potential energy does a 1.5-kg book gain when it's elevated 2 m? When it's elevated 4m? (Let g=10 N/kg)
9. 4000j
How much work is required to increase the kinetic energy of a motor scooter by 4000 J.
9. 1L container half submerged in the water displaces .5L of water. water density= 1g/cm^3; .5L=500ml=500cm^3. 1g/cm^3 x 500cm^3=500g= .5kg. weight=Fg=mg= (.5kg) (10m/s^2) = 5N
If a 1-L container is immersed halfway in water what is the volume of water displaced? What is the buoyant force on the container?
7. The ball will hit the bat with 1000 N force.
If a bat hits a ball with 1000N of force, with how much force does the ball hit back on the bat?
2. Air bags increase the time the force is applied and decrease the force, so the result is a lesser force for a longer duration.
In terms of impulse and momentum, why do air bags in cars reduce the chances of injury in accidents?
3. Poke or kick the boxes. The one that more greatly resists a change in motion is the one with the greater mass—the one filled with sand.
In the orbiting space shuttle you are handed two identical boxes, one filled with sand and the other filled with feathers. How can you tell which is which without opening the boxes?
9. The acceleration produced by a given force is inversely proportional to the mass.
Is acceleration directly proportional to mass, or is it inversley propotional to mass?
7. According to the Newton's law of gravitation force is directly proportional to the product of masses and inversely to the square of distance between them. Thus it is also called as inverse square law. here F = Gmm'/R^2 m = mass of earth m' = mass of the moon. Here F is same for both with which moon attracts earth or with which earth attracts moon.
The Earth and the Moon are attracted to each other by gravitational force. Does the more massive Earth attract the less massive Moon with a force that is greater, smaller, or the same as the force with which the Moon attracts the EArth?
14. To get to shore, the person may throw keys or coins or an item of clothing. The momentum of what is thrown will be accompanied by the thrower's oppositely directed momentum. So one can recoil towards shore. (Or inhale facing the shore and exhale facing away.)
A fully dressed person is at rest in the middle of a pond on perfectly frictionless ice and must get to shore. How can this be accomplished?
11. The crate would fall behind the car.
A heavy crate accidentally falls from a high-flying airplane just as it flies directly above a shiny red sprots car parked in a car lot. Relativ to te car, where will the crate crash?
6. Its momentum is the same (its weight might change, but not its mass).
A lunar vehicle is tested o Earth at a speed of 10 km/h. When it travels as fast on the Moon, is its momentum more, less, or the same?
10. A three times as fast car has 4(2) or 16 times the KE.
A moving car has kinetic energy. If it speeds up until it is going four times as fast, how much kinetic energy does it have in comparison?
2. Acceleration = net force/mass a = (20 m/s - 8 m/s)/ (4 s) a= 3 m/s squared
Calculate the acceleration of a bike that goes form 8m/s to 20 m/s in 4 s. Acceleration=net force/mass
9. (A) F = 3.5 x 10^22 N The obstetrician exerts about twice as much gravitational force.
Calculate the force of gravity bewttn the physician and the newborn baby.
3. Ft = (10N)(5s) = 50Ns
Calculate the impulse the occurs when an average force of 10 N is exerted on a cart for 5 s.
1. momentum = mass x velocity = 10 kg x 3m/s = 30kgm/s
Calculate the momentum of a 10-kg bowling ball rolling at 3 m/s.
7. KE= (1/2)mv^2 (1/2)1x6^2 (1/2)36 18J
Calculate the number of joules of kinetic energy a 1-kg parrot has when it flies at 6 m/s.
5. 30/10.33= 2.094162633 300000 N/m^2;
Calculate the water pressure at the base of a 30-m-tall water tower.
3. Power = Change in Energy / time elapsed = 2J / 1s = 2W.
Calculate the watts of power expended when a force of 1 N moves a book 2 m in a time interval of 1 s.
1. W=Fd= (2N)(3m)=6 N.m= 6J
Calculate the work done when a force of 2 N moves a book 3 m.
Average Speed= 100/10
Calculate your average speed if you run 100 meters in 10 seconds.
3. GPE is at a max at the height of it's trajectory. KE is at a maximum when it leaves your hand, or, on it's downward path, just before it hits the ground.
Consider a ball thrown straight up in the air. At what position is its kinetic energy a maximum? Where is its gravitational potential energy a maximum?
5. F= ma (30,000 kg) * (4 m/s^2) 120,000 kg * m/s^2 120,000 N
Consider a jumbo jet of mass 30,000 kg in takeoff when the thrust from each of four engines is 30,000 N. Who that its accelration is 4 m/s^2
It should be "constant speed". It is impossible to round a curve at constant velocity since your are changing directions.
Correct your friend who says, "The race-car driver rounded the curve at a constant velocity of 100 km/h."
A bowling ball rolling at constant velocity is in equilibrium until it hits the pins.
Give an example of something moving when a net force of zero acts on it
The raw egg may resume spinning but the cooked egg will not. Explain.Hard-boiled eggs are solid inside. In the raw egg, the liquid inside the egg slides about and stops the egg from spinning as fast. When you stop the hard-boiled egg, it stops quickly. When you stop the raw egg, it keeps turning a little bit.
The raw egg may resume spinning but the cooked egg will not. Explain.
There is a total of 200 N + 200 N = 400 N pulling UP and a total of 250 N + W pulling DOWN. The net force is zero because the system is in equilibrium. That means the force DOWN must equal the force UP or 250 N + W= 400 N. W= 150 N.
The sketch shows a painting scaffold in mechanical equilibrium. The person in the middle weighs 250 N, and the tnesions in each rope are 200 N What is the weight of the scaffold?
16. The greater mass offsets the equally greater force; whereas force tends to accelerate things, mass tends to resist acceleration.
why doesn't a heavy object accelrate more than a light object when both are freely falling?
3. Ft = change in mv 1149 F = change mv 1151 (75kg)(25m/s)/0.1s = 18750N
A car carrying a 75-kg test dummy crashes into a wall at 25 m/s and is brought to rest in 0.1 s. Show that the average force exerted by the seat elt on the dummy is 18,750 N.
6. Let m be the mass of the freight car, and 4m the mass of the diesel engine, and v the speed after both have coupled together. Before collision, the total momentum is due only to the diesel engine, 4m (5 km/h), because the momentum of the freight car is 0. After collision, the combined mass is (4m + m), and combined momentum is (4m + m)v. By the conservation of momentum equation: Momentum before = momentum after 4m (5 km/h) + 0 = (4m + m)v (20 ·km/h) =4 km/h
A railroad diesel engine weighs four times as much as a freight car. If the diesel engine coasts at 5 km/h into a freight car that is initially at rest, show that the speed of the coupled cars is 4 km/h.
18. When it slows to a point where it no longer recedes and begins to falls back toward earth it greatest speed. The speed lost in receding is regained as it falls back toward the earth. Greatest speed nearest earth-slowest speed farthest away.
At what part of an elliptical orbit does a satellite have the greatest speed? the least speed?
12. D=m/vol D~1/vol 1/2 vol=2x density
By how much does the density of air increase when it is compressed to half its volume? Its pressure?
Speed is the distance covered per unit of time.Velocity is the speed and direction of an object. Basically, speed is a description of how fast; velocity is how fast and in what direction.
Distinguish between speed and velocity
1. Acceleration is a change in speed, a change in direction, or a change in both speed and direction. Velocity is the speed of something in a given direction.
Distinguish between velocity and acceleration
Did the entire stack of coins move or just one coin move?
Explain in terms of inertia.Because of inertia, an object at rest will remain that way unless acted on by an outside force. When you flicked the coin, only the coin that was hit was moved. The others will fall in place. Same trick as when a waiter yanks a tablecloth quickly, but the dishes stay in place on the table.
The boiled egg rolled the fastest, because of the fact it's solid on the inside. In a raw egg, the yolk and white will be 'sloshing' around, trying to catch up to the shell, therefore slowing down the total velocity.
Explain why the raw egg wobbled and spun slowly while the cooked egg spun rapidly.
3. It is g = GM/r2 = (6.67 x 10-11) (3.0 x 1030)/(8.0 x 103) 2 = 3. 1 x 10^12 m/s2, 300 billion times g on Earth.
Find the change in the force of gravity between two planets when their masses remain the same but he distance between them is increases by ten times.
30 N + 20 N= 50 N
Find the net force produced by a 30-N and 20-N force in each of the following cases: (A) both forces act in the same direction.
12. If we're assuming there is no air resistance, then while her potential energy decreases by 1000J, there also must be an energy increase by 1000J. If 900J already increased, that leaves you with 100J to thermal energy.
On a slide a child has potential energy that decreases by 1000 j while her kinetic energy increases by 900 j. What other form of energy is involved, and how much?
14. The Earth does not fall into the sun because it is moving fast enough around it. Imagine a weight on the end of a string like a conker, with the weight being the earth, and where you hold the string being the sun. If you swing it around fast enough, the weight spins in circles and does not go near your hand, but if you swing it slowly, the weight will fall in. So because the earth is spinning fast enough around the sun, it does not fall in.
Since Earth is gravitationally attracted to the Sun, why don't we simply crash into the Sun?
1. it has less distance to travel
Suppose that you balance a 5-kg ball on the tip of your finer, which has an area of 1cm^2. Show that the pressure on your finger is 50 N/cm^2, which is 500kPa.
10. According to Newton's Third Law, the forces on these two masses must be equal (and in opposite directions). According to Newton's Second Law, F = m a, we find a = F / m. That means the acceleration of the twice-as-massive cart will be one-half the acceleration of the other.
Suppose two carts, one twice as massive a sthe other, fly apart when the compressed spring that joins themis relased. How fast does the heavier cart roll compared to the lighter cart?
3. Therefore the stopping distance is proportional to the square of the velocity, and if you are going twice as fast, you require four times the stopping distance! Applying this to our particular problem, the stopping distance at 50 km/h is 15 m. If we increase speed to 150 km/h (three times the initial speed) we expect the stopping distance to rise by three squared, or nine times. Therefore the expected stopping distance is 9 × 15 = 135 m.
This question is typical on some driver's license exams: A car moving at 50 km/h skids 15 m with locked brakes. How far will the car skid with locked brakes at 150 km/h?
16. Momentum is the same for both, so the twice-as-heavy player would have to be moving at half the speed of the higher player.
Two football players have a head-on collision and both stop short in their paths. If one player is twice as heavy as the other, how does his speed compare to the smaller player?
14. They are not in free fall. Like the parachutists, the heavier ball will have to fall faster before air drag builds up to weight, so it will fall faster through the air. Even if terminal velocity isn't reached, the heavier one will accelerate more than the light one.
Two pumpkins are dropped from a high building through the air. One pumpkin is hollow and the other filled with rocks. Which accelerates more?
5. Newton's law of gravitation F=m1*m2/r^2 R is the distance between the two objects Therefore, if r is doubled, the effect is squared (because r is squared in the equation) 2^2=4 So, the force F, is reduced to a fourth of the force before the doubling
how does the force of gravity between two bodies change when the distance between them is doubled?
11. 100 tons
what weight of water is displaced by a 100-ton floating ship? WHat is the buoyant force that acts on this ship?
