midterm

It takes Harry 35s to walk from x= -12m to x= -47m. What is his velocity? (1.13 P)

- 1.0 m/s

You are driving on the highway, and you come to a steep downhill section. As you roll down the hill, you take your foot off the gas pedal. You can ignore friction, but you can't ignore air resistance. (4.37 P)

-drag opposite of car on slope -normal force up/right -weight down

Your car is skidding to a stop from a high speed. (4.34 P)

-normal force up -weight down -kinetic friction to the left -drag to the left

An ascending elevator, hanging from a cable, is coming to a stop. (4.36 P)

-tension up -weight down (larger)

A car coasts at a constant speed over a circular hill. Which of the free-body diagrams in Figure Q6.11 is correct? Explain. (6.11 C)

1) downward 2) downward 3) C 4) downward 5)upward 6) downward

The forces in figure are acting on a 2.0 kg object. What is a_x , the x-component of the object's acceleration? Give a step by step solution. (5.10 P)

1.0 m/s2

Anna is running to the right, as shown in the figure. Balls 1 & 2 are thrown toward her by friends standing on the ground. According to Anna, both balls are approaching her at the same speed. Which ball was thrown with the faster speed? Or were they thrown with the same speed? Explain. (3.19 C)

NO, the balls don't have the same speed. BALL 1 is faster

If you kick a football, at what angle to the ground should you kick the ball for the maximum range—that is, the greatest distance down the field? At what angle to the ground should you kick the ball for the maximum "hang time"—that is, the maximum time in the air? (3.8 C)

a) 45 degrees b) 90 degrees

One simple model for a person running the 100 m dash is to assume the sprinter runs with constant acceleration until reaching top speed, then maintains that speed through the finish line. If a sprinter reaches his top speed of 11.52 m/s in 2.14 s, what will be his total time? Express your answer in seconds. (2.43 P)

10.0 s

Excellent human jumpers can leap straight up to a height of 110 cm off the ground. To reach this height, with what speed would a person need to leave the ground? (2.51 P)

4.6 m/s

A position vector with magnitude 10 m points to the right and up. Its x-component is 6.0 m. What is the value of its y-component? (3.5 P)

8.0 m

A 1500 kg car drives around a flat 200-m-diameter circular track at 25 m/s. What are the magnitude and direction of the net force on the car? What causes this force? (6.17 P)

9400 N, toward center, static friction

The figure showed data for the speed of blood in the aorta. Determine the magnitude of the acceleration for both phases, speeding up and slowing down. (2.24 P)

a up= 15 m/s2 a down= -5 m/s2

Alan leaves Los Angeles at 8:00 am to drive to San Francisco, 400 mi away. He travels at a steady 50 mph. Beth leaves Los Angeles at 9:00 am and drives a steady 60 mph. a) Who gets to San Francisco first? b) How long does the first to arrive have to wait for the second? (2.11 P)

a) Beth b) 20 min

A softball player hits the ball and starts running toward first base. Draw a motion diagram, using the particle model, showing her velocity vectors during the first few seconds of her run. (1.11 C)

diagram

Keira starts at position x = 23 m along a coordinate axis. She then undergoes a displacement of -45 m. What is her final position? (1.7 P)

-22 m

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? (4.10 C)

-mass of jonathan is more than his daughter so force experienced by him is greater. -acceleration is same for both -so back of seat exert a greater force on JONATHAN

Suppose you are holding a box in front of you and away from your body by squeezing the sides, as shown in Figure Q5.10. Draw a free-body diagram showing all of the forces on the box. What is the force that is holding the box up, the force that is opposite the weight force?(5.10 C)

-static friction up -weight down -normal force goes left and right on sides

A girl is swinging on a rope. Identify the forces acting on the girl at the very top of her swing. (4.7 P)

-tension going up the rope -centripetal force going to the side -weight going down

A box is being dragged across the floor at a constant speed by a rope pulling horizontally on it. Friction is not negligible. (4.39 P)

-weight down -normal force up -tension right -kinetic friction left

A skier is sliding down a 15° slope. Friction is not negligible. Identify the forces on the skier. (4.11 P)

-weight going down -kinetic friction going the opposite of skier -normal force going up/right

Two workers are sliding a 300 kg crate across the floor. One worker pushes forward on the crate with a force of 380 N while the other pulls in the same direction with a force of 350 N using a rope connected to the crate. Both forces are horizontal, and the crate slides with a constant speed. What is the crate's coefficient of kinetic friction on the floor? (5.27 P)

.25

shows an object's acceleration-versus-force graph. What is the object's mass? (4.21 P)

.25 kg

A typical running track is an oval with 74-m-diameter half circles at each end. A runner going once around the track covers a distance of 400 m. Suppose a runner, moving at a constant speed, goes once around the track in 1 min 40 s. What is her centripetal acceleration during the turn at each end of the track? (6.12 P)

.43 m/s2

In major league baseball, the pitcher's mound is 60 feet from the batter. If a pitcher throws a 95 mph fastball, how much time elapses from when the ball leaves the pitcher's hand until the ball reaches the batter? (2.9 P)

.43 s

A security guard walks at a steady pace, traveling 110 m in one trip around the perimeter of a building. It takes him 240 s to make this trip. What is his speed? (1.10 P)

.46 m/s

In a head-on collision, an infant is much safer in a child safety seat when the seat is installed facing the rear of the car. Explain. (4.3 P)

1. As the child rides in the seat, his/her head and back rest against the padded back of the seat. If the car is brought to a rapid stop (as in a head-on collision) the child will continue to move FORWARD at the before-crash speed until he/she hits something. 2. The object hit is the back of the seat (supporting the entire back and head) which is padded and as a result the force INCREASES to the maximum value over a time interval. 3. Granted this time interval may be SMALL but that is considerably better than instantaneous. Also since the head is supported, there will be NO WHIPLASH

A pipe discharges storm water into a creek. Water flows horizontally out of the pipe at 1.5 m/s, and the end of the pipe is 2.5 m above the creek. How far out from the end of the pipe is the point where the stream of water meets the creek? (3.29 P)

1.1 m

A cross-country skier is skiing along at a zippy 8.0 m/s. She stops pushing and simply glides along, slowing to a reduced speed of 6.0 m/s after gliding for 5.0 m. What is the magnitude of her acceleration as she slows? (2.33 P)

2.8 m/s2

You begin sliding down a 15∘ ski slope. Ignoring friction and resistance, how fast will you be moving after 10 s?(3.16 P)

25.4 m/s

A compact car has a maximum acceleration of 4.0 m/s2 when it carries only the driver and has a total mass of 1200 kg. What is its maximum acceleration after picking up four passengers and their luggage, adding an additional 400 kg of mass? (4.15 P)

3.0 m/s2

A 5.0-m-diameter merry-go-round is turning with a 4.0 s period. What is the speed of a child on the rim? (6.1 P)

3.9 m/s

Loveland, Colorado, is 18 km due south of Fort Collins and 31 km due west of Greeley. What is the distance between Fort Collins and Greeley? (1.26 P)

36 km

Formula One racers speed up much more quickly than normal passenger vehicles, and they also can stop in a much shorter distance. A Formula One racer traveling at 90 m/s can stop in a distance of 110 m. What is the magnitude of the car's acceleration as it slows during braking? (2.35 P)

37 m/s2

The most dangerous particles in polluted air are those with diameters less than 2.5 um because they can penetrate deeply into the lungs, A 15-cm-tall closed container holds a sample of polluted air containing many spherical particles with a 2.5 um and a mass of 1.4 x 10-14 kg. How long does it take for all of the particles to settle to the bottom of the container? (5.37 P)

4.6 x 10^2 s = 7.7 min

A 4000 kg truck is parked on a 7.0° slope. How big is the friction force on the truck? (5.28 P)

4800 N

A city has streets laid out in a square grid, with each block 135 m long. If you drive north for three blocks, then west for two blocks, how far are you from your starting point? (1.27 P)

487 m

A gannet is a seabird that fishes by diving from a great height. If a gannet hits the water at 32 m/s (which they do), what height did it dive from? Assume that the gannet was motionless before starting its dive. (2.47 P)

52 m

car traveling at 30 m/s runs out of gas while traveling up a 5 degree slope. How far will it coast before starting to roll back down? (3.17 P)

530 m

What is the tension in the rope of Figure P5.44? man=60 kg box=100 kg (5.44 P)

588 N

A 55 kg ice skater is gliding along at 3.5 m/s. Five seconds later her speed has dropped to 2.9 m/s. What is the magnitude of the kinetic friction acting on her skates? (4.25 P)

6.6 N

The figure is a somewhat simplified velocity graph for Olympic sprinter Carl Lewis starting a 100 m dash. Estimate his acceleration during each of the intervals A, B, and C. (2.25 P)

A= 6.1 m/s2 B= 2.5 m/s2 C= 1.5 m/s2

Three arrows are shot horizontally. They have left the bow and are traveling parallel to the ground as shown in the figure. Air resistance is negligible. (4.4 C)

F1 = F2 = F3 = 0 because there is no change in the horizontal motion of the arrows.

Mountain goats can easily scale slopes angled at 60∘ from horizontal. What is the normal force & static friction acting on a mountain goat that weighs 900 N and is standing on such a slope? (5.24 P)

Fn= 450 N Fs= 780 N

Why is it impossible for an astronaut inside an orbiting space station to go from one end to the other by walking normally? (6.17 C)

In an orbiting station, after one foot pushes off there isn't a force to bring the astronaut back to the "floor" for the next step.

Suppose two vectors have unequal magnitudes. Can their sum be 0→? Explain. (3.3 C)

No. For 2 vectors to equal 0, they would have to be of equal magnitude and opposite directions.

Mark and Sofia walk together down a long, straight road. They walk without stopping for 4 miles. At this point Sofia says their displacement during the trip must have been 4 miles; Mark says their current position must be 4 miles. Who, if either, is correct? Explain. (1.5 C)

Sophia & Mark, only if their starting point is the origin of a coordinate system

The three ropes in the figure are tied to a small, very light ring. Two of the ropes are anchored to walls at right angles, and the third rope pulls as shown. What are T1 and T2, the magnitudes of the tension forces in the first two ropes? (5.1 P)

T1= 87 N T2= 50 N

If you go to a ski area, you'll likely find that the beginner's slope has the smallest angle. Use the concept of acceleration on a ramp to explain why this is so. (3.11 C)

The lower the angle of the slope, the LOWER the acceleration down the slope since acceleration along a ramp is given by G SIN THETA Furthermore, the speed of the bottom of the slope will be less if acceleration is LESS. a LOWER angle gives the skier a LOWER velocity and, consequently, better control.

Suppose you are an astronaut on a spacewalk, far from any source of gravity. You find yourself floating alongside your spacecraft but 10 m away, with no propulsion system to get back to it. In your tool belt you have a hammer, a wrench, and a roll of duct tape. How can you get back to your spacecraft? (4.11 C)

Throw the items away from the spaceship.

showed a situation in which the force of the road on the car's tire points forward. In other situations, the force points backward. Give an example of such a situation. (4.16 C)

When the car is going forward and slowing down

Suppose that, while in a squatting position, you stand on your hands, and then you pull up on your feet with a great deal of force. You are applying a large force to the bottoms of your feet, but no matter how strong you are, you will never be able to lift yourself off the ground. Use your understanding of force and motion to explain why this is not possible. (4.20 C)

You can't lift yourself off the floor because the net external force on you is still zero.

Convert the following to SI units: a) 8.0 in b) 66 ft/s c) 60 mph (1.17 P)

a) .20 m b) 20 m/s c) 27 m/s

A ball with a horizontal speed of 1.25 m/s rolls of a bench 1.00 m above the floor. a) How long will it take the ball to hit the floor? b) How far from a point on the floor directly below the edge of the bench will the ball land? (3.28 P)

a) .452 s b) .565 m

A horizontal rope is tied to a 50 kg box on frictionless ice. What is the tension in the rope if a) The box is at rest? b) The box moves at a steady 5.0 m/s? c) The box has vx=5.0m/s & ax=5.0m/s2 (5.12 P)

a) 0 b) 0 c) 250 N

Racing greyhounds are capable of rounding corners at very high speeds. A typical greyhound track has turns that are 45-m-diameter semicircles. A greyhound can run around these turns at a constant speed of 15 m/s. What is its acceleration in m/s2m/s2 and in units of g?(3.37 P)

a) 10 m/s2 b) 1.0 g

A constant force is applied to an object, causing the object to accelerate at 8.0 m/s2. What will the acceleration be if a) The force is doubled? b) The object's mass is doubled? c) The force and the object's mass are both doubled? d) The force is doubled and the object's mass is halved?(4.17 P)

a) 16 m/s2 b) 4.0 m/s2 c) 8.0 m/s2 d) 32 m/s2

One kind of baseball pitching machine works by rotating a light and stiff rigid rod about a horizontal axis until the ball is moving toward the target. Suppose a 144 g baseball is held 85 cm from the axis of rotation and released at the major league pitching speed of 85 mph. a) What is the ball's centripetal acceleration just before it is released? b) What is the magnitude of the net force that is acting on the ball just before it is released? (6.19 P)

a) 1700 m/s2 b) 240 N

shows Sue along the straight-line path between her home and the cinema. What is Sue's position x if a) Her home is the origin? b) The cinema is the origin? (1. 4 P)

a) 2 mi b) -3 mi

a) What constant acceleration, in SI units, must a car have to go from zero to 60 mph in 10 s? b) What fraction of g is this? c) How far has the car traveled when it reaches 60 mph? Give your answer both in SI units & feet. (2.29 P)

a) 2.7 m/s2 b) .27 g c) 134 m, 440 ft

A car is traveling at a steady 80 km/h in a 50 km/h zone. A police motorcycle takes off at the instant the car passes it, accelerating at a steady 8.0 m/s2. a) How much time elapses before the motorcycle is moving as fast as the car? b) How far is the motorcycle from the car when it reaches this speed? (2.41 P)

a) 2.8 s b) 31 m

The horse on a carousel is 4.0 m from the central axis. a) If the carousel rotates at 0.10 rev/s, how long does it take the horse to go around twice? b) How fast is a child on the horse going (in m/s)? (6.6 P)

a) 20 s b) 2.5 m/s

How many significant figures does each of the following numbers have? a) 6.21 b) 62.1 c) 0.620 d) 0.062 (1.19 P)

a) 3 b) 3 c) 3 d) 2

What is the free-fall acceleration at the surface of (a) Mars and (b) Jupiter? (6.43 P)

a) 3.77 m/s2 b) 25.9 m/s2

A 2200 kg truck has put its front bumper against the rear bumper of a 2400 kg SUV to give it a push. With the engine at full power and good tires on good pavement, the maximum forward force on the truck is 18,000 N. a) What is the maximum possible acceleration the truck can give the SUV? b) At this acceleration, what is the force of the SUV's bumper on the truck's bumper? (5.42 P)

a) 3.91 m/s2 b) 9384 N

Squid use jet propulsion for rapid escapes. A squid pulls water into its body and then rapidly ejects the water backward to propel itself forward. A 1.5 kg squid (not including water mass) can accelerate at 20 m/s2 by ejecting 0.15 kg of water. a) What is the magnitude of the thrust force on the squid? b) What is the magnitude of the force on the water being ejected? c)What acceleration is experienced by the water? (4.46 P)

a) 30 N b) 30 N c) 200 m/s2

Jack and Jill ran up the hill at 3.0 m/s. The horizontal component of Jill's velocity was 2.5 m/s a) What was the angle of the hill? b) What was the vertical component of Jill's velocity? (3.14 P)

a) 34 degrees b) 1.7 m/s

A particle rotates in a circle with centripetal acceleration a=8.0m/s2. What is a if? a) The radius is doubled without changing the particle's speed? b) The speed is doubled without changing the circle's radius? (3.41 P)

a) 4.0 m/s2 b) 32 m/s2

An early submersible craft for deep-sea exploration was raised and lowered by a cable from a ship. When the craft was stationary, the tension in the cable was 6000 N. When the craft was lowered or raised at a steady rate, the motion through the water added an 1800 N drag force. a) What was the tension in the cable when the craft was being lowered to the seafloor? b) What was the tension in the cable when the craft was being raised from the seafloor? (5.6 P)

a) 4200 N b) 7800 N

The centers of a 10 kg lead ball and a 100 g lead ball are separated by 10 cm. What gravitational force does each exert on the other? What is the ratio of this gravitational force to the weight of the 100 g ball? (6.34 P)

a) 6.67 x 10^-9 N b) 6.81 x 10^-9

The figure shows a graph of actual position-versus-time data for a particular type of drag racer known as a "funny car." a) Estimate the car's velocity at 2.0 s. b) Estimate the car's velocity at 4.0 s. (2.20 P)

a) 750 m/s b) 133 m/s

Convert the following to SI base units: a) 9.12 μs b) 3.42 km c) 44 cm/ms d) 80 km/h (1.16 P)

a) 9.12 x 10^-6 s b) 3.42 x 10^3 m c) 4.4 x 10^2 m/s d) 22.2 m/s

The figure below shows an object's position-versus-time graph. The letters A to E correspond to various segments of the motion in which the graph has constant slope. a) Write a realistic motion short story for an object that would have this position graph. b) In which segment(s) is the object at rest? c) In which segment(s) is the object moving to the right? d) Is the speed of the object during segment C greater than, equal to, or less than its speed during segment E? Explain (2.10 C)

a) A car is moving towards positive direction(A), then it comes to rest for some time (B), then it starts moving in negative direction (C) & reaches starting point, it comes to rest (D) & then moves in negative direction (E) b) B & D c) A d) greater than

a) Give an example of a vertical motion with a positive velocity and a negative acceleration. b) Give an example of a vertical motion with a negative velocity and a negative acceleration. (2.2 C)

a) A tossed ball on its way upward. As the ball moves upward it is slowing down, hence the acceleration is opposite the velocity (negative). b) A tossed ball on its way down. As the ball moves down it is speeding up, hence the acceleration is pointing in the same direction as the velocity (negative).

Are the objects described here in static equilibrium, dynamic equilibrium, or not in equilibrium at all? a) A girder is lifted at constant speed by a crane. b) A girder is lowered by a crane. It is slowing down. c) You're straining to hold a 200 lb barbell over your head. d) A jet plane has reached its cruising speed and altitude. e) A rock is falling into the Grand Canyon. f) A box in the back of a truck doesn't slide as the truck stops. (5.2 C)

a) Dynamic equilibrium b) NOT in equilibrium c) static equilibrium d) dynamic equilibrium e) NOT in equilibrium state f) NOT in equilibrium

The forces in the figure are acting on a 2.0 kg object. Find the values of ax, and ay, the x- and y-components of the object's acceleration. (5.11 P)

ay= 0.0 m/s2 ax= 1.0 m/s2

In Figure Q5.21, block 2 is moving to the right. There is no friction between the floor and block 2, but there is a friction force between blocks 1 and 2. In which direction is the kinetic friction force on block 1? On block 2? Explain. (5.21 C)

block 1: fk goes right opposite V block 2: fk goes left opposite V direction of kinetic force is always opposite the direction in which the object slides on the surface

Janelle stands on a balcony, two stories above Michael. She throws one ball straight up and one ball straight down, but both with the same initial speed. Eventually each ball passes Michael. Which ball, if either, is moving faster when it passes Michael? Explain. (2.9 C)

both balls have the same speed

A car travels to the left at a steady speed for a few seconds, then brakes for a stop sign. Use the particle model to draw a motion diagram of the car for the entire motion described here. Number the dots in order, starting with zero. (1.2 C)

diagram

A skydiver jumps out of an airplane. Her speed steadily increases until she deploys her parachute, at which point her speed quickly decreases. She subsequently falls to earth at a constant rate, stopping when she lands on the ground. Draw a motion diagram, using the particle model, that shows her position at successive times and includes velocity vectors. (1.13 C)

diagram

You are driving down the road at a constant speed. Another car going a bit faster catches up with you and passes you. Draw a position graph for both vehicles on the same set of axes, and note the point on the graph where the other vehicle passes you. (2.5 C)

diagram

You are cycling around a circular track at a constant speed. Does the magnitude of your acceleration change? The direction? (3.15 C)

magnitude of acceleration is constant, but velocity changes in direction

In uniform circular motion, which of the following quantities are constant: speed, instantaneous velocity, centripetal acceleration, the magnitude of the net force? (6.2 C)

speed & the magnitude of net force

A ball on a string moves in a vertical circle as in Figure Q6.7. When the ball is at its lowest point, is the tension in the string greater than, less than, or equal to the ball's weight? Explain. (You may want to include a free-body diagram as part of your explanation.) (6.7 C)

tension is GREATER THAN balls resting weight.. + diagram

A car travels along a straight east-west road. A coordinate system is established on the road, with x increasing to the east. The car ends up 14 mi west of the origin, which is defined as the intersection with Mulberry Road. If the car's displacement was -23 mi, on what side of Mulberry Road did the car start? How far from the intersection was the car at the start? (1.8P)

the car started 9 mi east of Mulberry Road

The boxes in Figure Q5.3 are now sliding; both have μk = 0.35. Is the friction force on A larger than, smaller than, or equal to the friction force on B? Explain. (5.4 C)

the friction force on A is EQUAL TO the force of B because THE BOXES REMAIN AT REST

For a projectile, which of the following quantities are constant during the flight: x,y,vx​,vy​,v,ax​,ay​? Which of the quantities are zero throughout the flight? (3.5 C)

vx,ax,ay are constant ax is zero