Physics midterm burks

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

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

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?

- Jonathan

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

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

Figure P4.21 shows an object's acceleration-versus-force graph. What is the object's mass?

-.25 kg

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

-45 + 23= -22

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.

The lower the angle of s1ope lower the acceleration. The downward acceleration is gsin⊖. The speed of the bottom of the slope will be less if acceleration is less. Lower the angle for better control. lower the velocity for better control

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

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)

- 0 - 0 - 250 N

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

- 588 N

Your car is skidding to a stop from a high speed.

- 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.

- tension up - weight down (larger)

A softball player hit 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 nun .

. . . . .

A city has streets laid out in a square grid , with each block 135m long. If you drive north for 3 blocks , the west for 2 blocks , how far are you from your starting point?

D= (135) × (3^2+2^2)^0.5 = 487m

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

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.

a. A tossed ball on its way upward . b. a ball tossed on it way down

Loveland , Colorado is 18 KM due south of Fort Collins and 31 km due west of Greenly . What is the distance between Fort Collins and Greenly ?

d2 = 18^2 + 31^2 = 1285 D= 35.85 km

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

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

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)

- 20 s - 2.5 m/s

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)

- 3.91 m/s2 - 9384 N

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 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?

- 6.6 N

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

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)

- C

Three arrows are shot horizontally. They have left the bow and are traveling parallel to the ground as shown in Figure Q4.4. Air resistance is negligible. Rank in order, from largest to smallest, the magnitudes of the horizontal forces, and acting on the arrows. Some may be equal. State your reasoning.

- 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.

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

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

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.

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

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)

- dynamic equilibrium - NOT in equilibrium - static equilibrium - dynamic equilibrium - NOT in equilibrium - NOT in equilibrium

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 and magnitude of the net force

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 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

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

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?

- throw the items away from the space ship to propel yourself back towards the spaceship

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

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

Figure 4.30b 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.

- when a car is going forward and slowing down. There is some net backward force on car

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.

- you can't lift yourself off the floor because there is still a net external force still on you that is 0

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?

-3.0 m/s2

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

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

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

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

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

.458 m/s

In major league baseball , the pitcher's mound is 60ft 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?

0.431 s

It takes Harry 35s to walk from ✗= -12m to ✗= - 47m. What is his velocity?

1 m/s negative direction

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?

45 degrees

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 0 .

7••••3•••• 6542I0 stops @ 7 Brakes @ 3

Convert the following to SI units :

A. 8.0 in = 0.2032m b. 66ft / s = 20.1168 m/s C. 60 mph =26.8224 m/s I in= 0.0254 m 1 ft/s = 0.3048 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.

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

Suppose two vectors have unequal magnitudes. Can their sum be 0->? Explain

NO. The sum of 2 vectors can only be 0 if they are in opposite directions and have same magnitude

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?

Vx , ax , ay quantities are constant during the flight, ax is 0 throughout the flight

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

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. What is the magnitude of the thrust force on the squid? What is the magnitude of the force on the water being ejected? What acceleration is experienced by the water?

a) 30 N b) 30 N c) 200 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

Figure P1.4 shows sue along the straight-line path between her home and the cinema .whats is sues position x if a) Her home is the origin? x=+2 miles b) The cinema is the origin? x= -3mi

a) x=+2 miles b)x= -3mi

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 is, 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?

a. 2.78 sec

How many significant figures does each of the following have?

a. 6.21= 3 b. 62.I= 3 C. 0.620= 3 d. 0.062= 2

Convert the following to SI base units :

a. 9.12 us = 9.12 x 10^-6 sec b 3.42km = 3420 m c. 44cm/ms = 440m/Sec d 80km/h = 22.22 m/sec

Figure 2.10 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 as 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.

a. A car is moving towards positive direction (segment A) , then it rests for some time (segment B) then it starts moving in a negative direction (seg c) and reaches starting point, it comes to rest (seg D) and then moves in negative direction (E) b. B and D c. A speed of object during segment C is greater than segment E

Alan leaves Los Angeles at 8:00 a.m. 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 ?

a. beth b. 19.8 min

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

both will move at the same speed

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

magnitude of the acceleration does not change, but the direction does

A car travels along a straight east - west road . A coordinate system is established on the road, with × increasing to the east. The car ends 14 mi west of the is origin, which defined as the intersection with Mulberry road. if the cars displacement was -23mi. What side of Mulberry Road did the car start on? How far from the intersection displacement was the car at the start?

she was 9 mi east of the origin initialy

Mark and Sofia walk together down a long, straight road . They walk without stopping for 4 mi. At this point sofia says their displacement during the trip must have been 4 mi. Mark says their current position must be 4 mills . Who , it either, is connect? Explain .

sofia is correct for sure. Mark will be correct only if their starting point is the origin of a coordinate system .

Anna is running to the right. Balls 1 and 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.

the speed of ball 1 is greater than ball 2