physics midterm 2021

Two football players are pushing a 60 kgkg blocking sled across the field at a constant speed of 2.0 m/sm/s. The coefficient of kinetic friction between the grass and the sled is 0.30. Once they stop pushing, how far will the sled slide before coming to rest?

0.68 m

Some car manufacturers claim that their vehicles could climb a slope of 44 ∘. For this to be possible, what must be the minimum coefficient of static friction between the vehicle's tires and the road?

1.0

A car drives horizontally off a 75-m-high cliff at a speed of 29 m/s . Ignore air resistance. How far from the base of the cliff will the car hit?

110 m

Suppose a spacecraft orbits the moon in a very low, circular orbit, just a few hundred meters above the lunar surface. The moon has a diameter of 3500 kmkm, and the free-fall acceleration at the surface is 1.60 m/s2m/s2. How much time does it take for the spacecraft to complete one orbit?

110 min

A person walks briskly at 2.10 m/s . How much time will it take them to walk one mile?

12.8 min

Suppose you and a friend, each of mass 60 kgkg , go to the park and get on a 4.5-mm-diameter merry-go-round. You stand on the outside edge of the merry-go-round, while your friend pushes so that it rotates once every 6.5 seconds. What is the magnitude of the (apparent) outward force that you feel?

130 N

A car can go from 0 to 60 mph in 14 s . A second car is capable of twice the acceleration of the first car. Assuming that it could maintain the same acceleration at higher speeds, how much time will this second car take to go from 0 to 120 mph?

14 s

A ball thrown at an initial angle of 37.0∘ and initial velocity vi = 24.0 m/s reaches a maximum height h, as shown in (Figure 1). With what initial speed must a ball be thrown straight up to reach the same maximum height h?

14.4

A cannon, elevated at 40∘ is fired at a wall 300 m away on level ground, as shown in the figure below. The initial speed of the cannonball is 89 m/s.(Figure 1) At what height h does the ball hit the wall?

160 m

Suppose a spacecraft orbits the moon in a very low, circular orbit, just a few hundred meters above the lunar surface. The moon has a diameter of 3500 kmkm, and the free-fall acceleration at the surface is 1.60 m/s2m/s2. How fast is this spacecraft moving?

1700 m/s

Free Fall on Different Worlds Objects in free fall on the earth have acceleration ay=−9.8m/s2ay=−9.8m/s2. On the moon, free fall acceleration is approximately 1/61/6 of the acceleration on earth. This changes the scale of problems involving free fall. For instance, suppose you jump straight upward, leaving the ground with velocity vivi and then steadily slowing until reaching zero velocity at your highest point. Because your initial velocity is determined mostly by the strength of your leg muscles, we can assume your initial velocity would be the same on the moon. But considering the equation h=v22gh=v22g we can see that, with a smaller free-fall acceleration, your maximum height would be greater. The following questions ask you to think about how certain athletic feats might be performed in this reduced-gravity environment. On the earth, an astronaut throws a ball straight upward; it stays in the air for a total time of 3.1 ss before reaching the ground again. If a ball were to be thrown upward with the same initial speed on the moon, how much time would pass before it hit the ground?

19 s

Suppose that the stone is launched with a speed of 3 m/sm/s and travels 40 mm before coming to rest. What is the approximate magnitude of the friction force on the stone?

2 N

A rider on a water slide goes through three different kinds of motion, as illustrated in the figure. Use the data and details from the figure to answer the following questions.(Figure 1) Suppose the designers of the water slide want to adjust the height above the water so that riders land twice as far away from the bottom of the slide. What would be the necessary height above the water?

2.4 m

Suppose one night the radius of the earth doubled but its mass stayed the same. What would be an approximate new value for the free-fall acceleration at the surface of the earth?

2.5 m/s/s

While standing in a low tunnel, you raise your arms and push against the ceiling with a force of 200 NN . Your mass is 80 kgkg. What force does the ceiling exert on you?

200 N

A football player at practice pushes a 70 kgkg blocking sled across the field at a constant speed. The coefficient of kinetic friction between the grass and the sled is 0.30. How much force must he apply to the sled?

210 N

The cylindrical space station in (Figure 1), ddd = 250 mm in diameter, rotates in order to provide artificial gravity of gg for the occupants. How much time does the station take to complete one rotation?

22 s

A truck is traveling at 30 m/sm/s on a slippery road. The driver slams on the brakes and the truck starts to skid. If the coefficient of kinetic friction between the tires and the road is 0.20, how far will the truck skid before stopping?

230 m

A bird flies 3.6 km due west and then 2.1 km due north. Another bird flies 2.1 km due west and 3.6 km due north.

29 degrees

Two cylindrical space stations, the second four times the diameter of the first, rotate so as to provide the same amount of artificial gravity. If the first station makes one rotation in the time TTT, then the second station makes one rotation in what time?

2T

A football is kicked at an angle of 40 ∘ with a speed of 24 m/s . To the nearest second, how long will the ball stay in the air

3 s

A 3.0 kg puck slides due east on a horizontal frictionless surface at a constant speed of 4.5 m/s . Then a force of magnitude 6.0 N , directed due north, is applied for 1.5 s . What is the northward component of the puck's velocity?

3.0 m/s

A rider on a water slide goes through three different kinds of motion, as illustrated in the figure. Use the data and details from the figure to answer the following questions.(Figure 1) What is the vertical component of the velocity of a rider as he or she hits the water?

3.4 m/s

Free Fall on Different Worlds Objects in free fall on the earth have acceleration ay=−9.8m/s2ay=−9.8m/s2. On the moon, free fall acceleration is approximately 1/61/6 of the acceleration on earth. This changes the scale of problems involving free fall. For instance, suppose you jump straight upward, leaving the ground with velocity vivi and then steadily slowing until reaching zero velocity at your highest point. Because your initial velocity is determined mostly by the strength of your leg muscles, we can assume your initial velocity would be the same on the moon. But considering the equation h=v22gh=v22g we can see that, with a smaller free-fall acceleration, your maximum height would be greater. The following questions ask you to think about how certain athletic feats might be performed in this reduced-gravity environment. If an astronaut can jump straight up to a height of 0.6 mm on earth, how high could he jump on the moon?

3.6 m

A car drives horizontally off a 75-m-high cliff at a speed of 29 m/s . Ignore air resistance. How long will it take the car to hit the ground?

3.9 s

Wings on race cars push them into the track. The increased normal force makes large friction forces possible. At one Formula One racetrack, cars turn around a half-circle with diameter 190 mm at 68 m/sm/s . For a 610 kgkg vehicle, the approximate minimum static friction force to complete this turn is

30000 N

A 2.5 kgkg ball is suspended by two light strings as shown in What is the tension TT in the angled string?

32 N

In the winter sport of curling, players give a 20 kgkg stone a push across a sheet of ice. The stone moves approximately 40 mm before coming to rest. The final position of the stone, in principle, only depends on the initial speed at which it is launched and the force of friction between the ice and the stone, but team members can use brooms to sweep the ice in front of the stone to adjust its speed and trajectory a bit; they must do this without touching the stone. Judicious sweeping can lengthen the travel of the stone by 3 mm. A curler pushes a stone to a speed of 3.0 m/sm/s over a time of 1.6 ss . Ignoring the force of friction, how much force must the curler apply to the stone to bring it up to speed?

38 N

A 4.5 kg dog sits on the floor of an elevator that is accelerating downward at 1.20 m/s2. What is the magnitude of the normal force of the elevator floor on the dog?

39 N

A cannon, elevated at 40∘ is fired at a wall 300 m away on level ground, as shown in the figure below. The initial speed of the cannonball is 89 m/s.(Figure 1) How long does it take for the ball to hit the wall?

4.4 s

A ball on a string moves around a complete circle, once a second, on a frictionless, horizontal table. The tension in the string is measured to be 10 NN . What would the tension be if the ball went around in only half a second?

40 N

Motor neurons in mammals transmit signals from the brain to skeletal muscles at approximately 25 m/s Estimate how much time in ms (10e−3 s) it will take for a signal to get from your brain to your hand.

40 ms

A 3.0 kg puck slides due east on a horizontal frictionless surface at a constant speed of 4.5 m/s . Then a force of magnitude 6.0 N , directed due north, is applied for 1.5 s . What is the speed of the puck?

5.4 m/s

A football is kicked at an angle of 35 ∘ with a speed of 24 m/s .

55 m

Eric has a mass of 70 kgkg. He is standing on a scale in an elevator that is accelerating downward at 1.7 m/s2m/s2. What is the approximate reading on the scale?

570 N

Suppose a plane accelerates from rest for 30 ss, achieving a takeoff speed of 80 m/sm/s after traveling a distance of 1200 mm down the runway. A smaller plane with the same acceleration has a takeoff speed of 56 m/sm/s . Starting from rest, after what distance will this smaller plane reach its takeoff speed?

588 m

The images of trees in the figure come from a catalog advertising fast-growing trees. If we mark the position of the top of the tree in the successive years, as shown in the graph in the figure, we obtain a motion diagram much like ones we have seen for other kinds of motion. The motion isn't steady, of course. In some months the tree grows rapidly; in other months, quite slowly. We can see, though, that the average speed of growth is fairly constant for the first few years.(Figure 1) At the end of year 3, a rope is tied to the very top of the tree to steady it. This rope is staked into the ground 15 feet away from the tree. What angle does the rope make with the ground?

63

Free Fall on Different Worlds Objects in free fall on the earth have acceleration ay=−9.8m/s2ay=−9.8m/s2. On the moon, free fall acceleration is approximately 1/61/6 of the acceleration on earth. This changes the scale of problems involving free fall. For instance, suppose you jump straight upward, leaving the ground with velocity vivi and then steadily slowing until reaching zero velocity at your highest point. Because your initial velocity is determined mostly by the strength of your leg muscles, we can assume your initial velocity would be the same on the moon. But considering the equation h=v22gh=v22g we can see that, with a smaller free-fall acceleration, your maximum height would be greater. The following questions ask you to think about how certain athletic feats might be performed in this reduced-gravity environment. On the earth, an astronaut can safely jump to the ground from a height of 1.3 mm ; her velocity when reaching the ground is slow enough to not cause injury. From what height could the astronaut safely jump to the ground on the moon?

7.8 m

A car is traveling at v_x = 24 m/s. The driver applies the brakes and the car decelerates at a_x = -4.0 m/se2 . What is the stopping distance?

72 m

The images of trees in the figure come from a catalog advertising fast-growing trees. If we mark the position of the top of the tree in the successive years, as shown in the graph in the figure, we obtain a motion diagram much like ones we have seen for other kinds of motion. The motion isn't steady, of course. In some months the tree grows rapidly; in other months, quite slowly. We can see, though, that the average speed of growth is fairly constant for the first few years.(Figure 1) What is the tree's speed in m/s?

9 * 10e-8

The images of trees in the figure come from a catalog advertising fast-growing trees. If we mark the position of the top of the tree in the successive years, as shown in the graph in the figure, we obtain a motion diagram much like ones we have seen for other kinds of motion. The motion isn't steady, of course. In some months the tree grows rapidly; in other months, quite slowly. We can see, though, that the average speed of growth is fairly constant for the first few years.(Figure 1) What is the tree's speed of growth, in feet per year, from t=1yr to t=3yr?

9 ft/yr

A rider on a water slide goes through three different kinds of motion, as illustrated in the figure. Use the data and details from the figure to answer the following questions.(Figure 1) At the end of the first section of the motion, riders are moving at what approximate speed?

9 m/s

The two block in (Figure 1) are at rest on frictionless surfaces. What must be the mass of the right block in order that the two blocks remain stationary? Suppose that mmm = 16 kgkg .

9.7 kg

While standing in a low tunnel, you raise your arms and push against the ceiling with a force of 200 NN . Your mass is 80 kgkg. What force does the floor exert on you?

980 N

(Figure 1) shows an acceleration-versus-force graph for three objects pulled by rubber bands. The mass of object 2 is 0.40 kg .

A larger slope implies a smaller mass. We know the mass of object 2, and we can find the other masses relative to m2 by comparing their slopes.

At which lettered point or points is the object slowing down?

A, E

The bacterium Escherichia coli (or E. coli), is a single-celled organism that lives in the gut of healthy humans and animals. When grown in a uniform medium rich in salts and amino acids, it swims along zig-zag paths at a constant speed. (Figure 1) shows the positions of an E. coli as it moves from point A to point J. Each segment of the motion can be identified by two letters, such as segment BC. During which segments, if any, does the bacterium have the same displacement?

AB and CD

The bacterium Escherichia coli (or E. coli), is a single-celled organism that lives in the gut of healthy humans and animals. When grown in a uniform medium rich in salts and amino acids, it swims along zig-zag paths at a constant speed. (Figure 1) shows the positions of an E. coli as it moves from point A to point J. Each segment of the motion can be identified by two letters, such as segment BC. During which segments, if any, does the bacterium have the same velocity?

AB and CD

The figure is a motion diagram with the clock reading (in seconds) shown at each position. The positions for t≥ 16 s are offset for clarity, but the motion actually occurs along a single track.(Figure 1) Which graph best represents the object's velocity? (Figure 2)

B - downward slop, horizontal, dashed vertical - horizontal

Which of the three drag racers had the greatest acceleration at t=0 s?

Betty

The figure below shows block A sitting on top of block B. A constant force F→ is exerted on block B, causing block B to accelerate to the right. Block A rides on block B without slipping.(Figure 1)

Block B exerts a friction force on block A, directed to the right.

Heather and Jerry are standing on a bridge 51 mm above a river. Heather throws a rock straight down with a speed of 17 m/sm/s . Jerry, at exactly the same instant of time, throws a rock straight up with the same speed. Ignore air resistance. Which rock has the faster speed as it hits the water?

Both rocks hit water with equal speeds.

The figure shows a position-versus-time graph. (Figure 1) At which lettered point or points is the object speeding up?

C

(Figure 1)Two cars travel on the parallel lanes of a two-lane road. The cars' motions are represented by the position versus time graph shown in the figure. Answer the questions using the times from the graph indicated by letters. At which of the times do the two cars pass each other?

D - when the lines intersect

The sweepers in a curling competition adjust the trajectory of the stone by

Decreasing the coefficient of friction between the stone and the ice.

A Porsche challenges a Honda to a 400 mm race. Because the Porsche's acceleration of 3.4 m/s2m/s2 is larger than the Honda's 3.0 m/s2m/s2, the Honda gets a 110 mm head start - it is only 290 mm from the finish line. Assume, somewhat unrealistically, that both cars can maintain these accelerations the entire distance Who wins the race?

Honda

A rider on a water slide goes through three different kinds of motion, as illustrated in the figure. Use the data and details from the figure to answer the following questions.(Figure 1) Suppose the acceleration during the second section of the motion is too large to be comfortable for riders. What change could be made to decrease the acceleration during this section?

Increase the radius of the circular segment.

You are going sledding with your friends, sliding down a snowy hill. Friction can't be ignored. Riding solo on your sled, you have a certain acceleration. Would the acceleration change if you let a friend ride with you, increasing the mass?

No, increasing the mass does increase the net force on the system, but it also increases the inertia. a=Fnetma=Fnetm. Since both the net force and mass are increased they still cancel, leaving the acceleration the same.

The rope can support a maximum tension of 6100 NN . Is this rope strong enough to do the job? Choose the correct answer and explanation.

No. The tension in the ropes exceeds the maximum value, the ropes will break.

Planet 1 has orbital radius r1r1 and planet 2 has r2=4r1r2=4r1. Planet 1 orbits with period T1T1. Planet 2 orbits with period

T2 = 8T1

Suppose the stone's mass is increased to 40 kg, but it is launched at the same 3 m/s. Which one of the following is true?

The force of friction would now be greater.

Is the magnitude of the net force on the ball greatest when it is going up or when it is on the way down? Or is it the same in both cases? Explain. Air resistance should not be neglected for a large, light object.

The only contact force is the force of air drag on the ball. The only long-range force is the weight of the ball. Drag always points in the direction opposite to the motion. Thus the weight of the ball and the drag force always reinforce each other if the ball is moving straight up. The net force is larger on the way up.

Scallops eject water from their shells to provide a thrust force. (Figure 1) shows a smoothed graph of actual data for the initial motion of a 25 gg scallop speeding up to escape a predator. You may want to review (Pages 110 - 111) . How does this force compare to the 0.25 NN weight of the scallop?

This force is 1/10 of the weight of the scallop.

An object moves along the x axis during four separate trials. Graphs of position versus time for each trial (with the same scales on each axis) are shown in the figure. (Figure 1) During which trial or trials is the object's velocity not constant? Check all that apply. View Available Hint(s)for Part A Trial A (linear slope upwards) Trial B (curve) Trial C (horizontal slope) Trial D (linear slope downwards)

Trial B

An object moves along the x axis during four separate trials. Graphs of position versus time for each trial (with the same scales on each axis) are shown in the figure. (Figure 1) During which trial or trials is the magnitude of the average velocity the largest? Trial A (linear slope upwards) Trial B (curve) Trial C (horizontal slope) Trial D (linear slope downwards)

Trial B (curve) and Trial D (linear slope downwards)

In 1780, in what is now referred to as "Brady's Leap," Captain Sam Brady of the U.S. Continental Army escaped certain death from his enemies by running over the edge of the cliff above Ohio's Cuyahoga River in (Figure 1), which is confined at that spot to a gorge. He landed safely on the far side of the river. It was reported that he leapt 22 ftft (≈≈ 6.7 mm) across while falling 20 ftft (≈≈ 6.1 mm). The world-record time for the 100 mm dash is approximately 10 ss. Given this, is it reasonable to expect Brady to be able to run fast enough to achieve Brady's leap?

Yes, the obtained speed is less than the world-record.

You are walking up an icy slope. Suddenly your feet slip, and you start to slide backward. Will you slide at a constant speed, or will you accelerate?

You will accelerate because the kinetic friction is less than the maximum static friction.

The bacterium Escherichia coli (or E. coli), is a single-celled organism that lives in the gut of healthy humans and animals. When grown in a uniform medium rich in salts and amino acids, it swims along zig-zag paths at a constant speed. (Figure 1) shows the positions of an E. coli as it moves from point A to point J. Each segment of the motion can be identified by two letters, such as segment BC. During which segments, if any, does the bacterium have the same speed?

all paths

The minimum stopping distance for a car traveling at a speed of 30 m/sm/s is 60 mm, including the distance traveled during the driver's reaction time of 0.50 ss . Select the correct position-versus-time graph for the motion of the car. Assume the car is at xixi = 0 mm when the driver first sees the emergency situation ahead that calls for a rapid halt.

arc starting from 0,0

Which of the quantities are zero throughout the flight?

ax

A person gets in an elevator on the ground floor and rides it to the top floor of a building. Choose a velocity-versus-time graph for this motion.

bell shaped

In an amusement-park ride, cars rolling along at high speed suddenly head up a long, straight ramp. They roll up the ramp, reverse direction at the highest point, then roll backward back down the ramp. Which way does their acceleration vector point

downward along the ramp

Choose the correct velocity-versus-time graph for a rock that is thrown straight upward, from the instant it leaves the hand until the instant it hits the ground.

downward linear slope

In which direction must the plane fly, east to west or west to east?

e to w

A student at the top of a building of height h throws ball A straight upward with speed v0 and throws ball B straight downward with the same initial speed. Compare the ball's accelerations, both direction and magnitude, immediately after they leave her hand. Is one acceleration larger than the other? Or are the magnitudes equal?

equal

A student at the top of a building of height h throws ball A straight upward with speed v0 and throws ball B straight downward with the same initial speed. Compare the final speeds of the balls as they reach the ground.

equal

If you are standing still, the upward normal force on you from the floor is equal in magnitude to the weight force that acts on you. But it's possible to move so that the normal force is greater than your weight.

if you jump up, during the initial phase when you are still in contact with the floor, you are accelerating upward. This means the net force on you must be upward, so the upward normal force must be bigger than the downward weight force.

Jonathan accelerates away from a stop sign. His eight-year-old daughter sits in the passenger seat. On whom does the back of the seat exert a greater force?

jonathon

A man's higher initial acceleration means that a man can outrun a horse over a very short race. A simple - but plausible - model for a sprint by a man and a horse uses the following assumptions: The man accelerates at 6.0 m/s2m/s2 for 1.8 ss and then runs at a constant speed. A horse accelerates at a more modest 5.0 m/s2m/s2 but continues accelerating for 4.8 ss and then continues at a constant speed. A man and a horse are competing in a 200 mm race. The man is given a 100 mm head start, so he begins 100 mm from the finish line. Who wins the race?

man

We set the origin of a coordinate system so that the position of a train is x = 0 m at t = 0 s. (Figure 1) shows the train's velocity graph. Choose the correct position graph for the train.

nike shaped graph

(Figure 1)Two cars travel on the parallel lanes of a two-lane road. The cars' motions are represented by the position versus time graph shown in the figure. Answer the questions using the times from the graph indicated by letters. Are the two cars traveling in the same direction when they pass each other?

no

Calculate the force which farmer needs to apply to budge the pig.

no, the farmer will not be able to budge the pig, because the maximum static friction force is greater than the farmer's maximum pull of 800 NN.

Shannon decides to check the accuracy of her speedometer. She adjusts her speed to read exactly 70 mphmph on her speedometer and holds this steady, measuring the time between successive mile markers separated by exactly 1.00 mile. If she measures a time of 47 s , is her speedometer accurate? If not, is the speed it shows too high or too low?

no, too low

In uniform circular motion, which of the following quantities are constant?

the magnitude of the net force speed

A rider on a water slide goes through three different kinds of motion, as illustrated in the figure. Use the data and details from the figure to answer the following questions.(Figure 1) During which section of the motion is the magnitude of the acceleration experienced by a rider the greatest?

the second

Chris is holding two softballs while standing on a balcony. She throws ball 1 straight up in the air and, at the same instant, releases her grip on ball 2, letting it drop over the side of the building. Which velocity graph best represents the motion of the two balls?

two downward slopes, 1 is above 2

(Figure 1) shows growth rings in the trunk of a pine tree. You can clearly see the wide and the narrow rings that correspond to years of fast and slow growth. You can think of these rings as a motion diagram for the growth of the tree. If we define an axis as shown, with xx measured out from the center of the tree, use the appearance of the rings to choose the correct velocity-versus-time graph for the radial growth of the tree.

u shaped

A 200 kgkg weather rocket is loaded with 100 kgkg of fuel and fired straight up. It accelerates upward at 30.0 m/s2m/s2 for 30.0 ss, then runs out of fuel. Ignore any air resistance effects. Choose the correct velocity-versus-time graph for the rocket from liftoff until it hits the ground.

upside down v

For a projectile, which of the following quantities are constant during the flight: x, y, vx, vy, v, ax, ay?

vx, ax, ay

A tennis player hits a ball 2.0 m above the ground. The ball leaves his racquet with a speed of 20 m/s at an angle 5.0 ∘ above the horizontal. The horizontal distance to the net is 7.0 m, and the net is 1.0 m high. Does the ball clear the net?

yes