Solving Together (HMWK) #1 on Chapter 1 PHYS 2425 Homework Problems–Choose 10 problems to complete

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Solving Together (HMWK) #1 on Chapter 1 PHYS 2425 Homework Problems–Choose 10 problems to complete. Circle numbers to distinguish your 10 chosen problems. (1-1) How many significant figures do each of the following numbers have: (a) 214 (b) 81.60 (c) 7.03 (d) 0.03 (e) 0.0086 (f) 3236 (g) 8700 (1-3) Write out the following numbers in full with the correct number of zeros: (a) 8.69 × 104 (b) 9.1 × 103 (c) 8.8 × 10−1 (d) 4.76 × 102 (e) 3.62 × 10−5 (1-5) What is the percent uncertainty in the measurement 5.48m ± 0.25m? (1-6) Time intervals measured with a stopwatch typically have an uncertainty of about 0.2 s, due to human reaction time at the start and stop moments. What is the percent uncertainty of a hand-timed measurement of (a) 5.5 s (b) 55 s (c) 5.5 min (1-7) Add (9.2 × 103 s) + (8.3 × 104 s) + (0.008 × 106 s). (1-8) Multiply 3.079 × 102 m by 0.068 × 10−1 m taking into account significant figures. (1-10) What, approximately, is the percent uncertainty in the volume of a spherical beach ball of radius r = 0.84 ± 0.04 m? (1-12) Write the following as full (decimal) numbers without prefixes on the units: (a) 286.6 mm (b) 85µV (c) 760 mg (d) 62.1 ps (e) 22.5 nm (f) 2.50 gigavolts (1-15) The Sun, on average, is 93 million miles from Earth. How many meters is this? Express (a) using powers of 10 (b) using a metric prefix (km) (1-18) Determine the conversion factor between (a) km/h and mi/h (b) m/s and ft/s (c) km/h and m/s (1-23) Use Table 1-3 to estimate the total number of protons or neutrons in (a) a bacterium (b) a DNA molecule (c) the human body (d) our Galaxy (1-26) Estimate how many books can be shelved in a college library with 3500 m2 of floor space. Assume 8 shelves high, having books on both sides, with corridors 1.5 m wide. Assume books are about the size of this one, on average. (1-32) You are in a hot air balloon, 20 m above the flat Texas plains. You look out toward the horizon. How far out can you see-that is, how far is your horizon? The Earth’s radius is about 6400 km. Extra Credit–Optional: Choose One (1-24) A standard baseball has a circumference of approximately 23 cm. If a baseball has the same mass per unit volume (see Tables in Section 1-5) as a neutron or a proton, about the what would its mass be? (1-30) Estimate the number of gallons of gasoline consumed by the total of all automobile drivers in the U.S., per year. Solving Together #2 on Chapter 2 PHYS 2425 Homework Problems–Choose 10 problems to complete. Circle numbers to distinguish your 10 chosen problems. (2-4) A rolling ball moves from x1 = 8.4cm t x2 = −4.2cm during the time from t1 = 3.0s to t2 = 6.1s. What is its average velocity over this time interval? (2-11) A car traveling 95 km/h is 210 m behind a truck traveling 75 km/h. How long will it take the car to reach the truck? (2-12) Calculate the average speed and average velocity of a complete round trip in which the outgoing 250km is covered at 95km/h, followed by a 1.0 hour lunch break, and then return 250km is covered at 55km/h. (2-18) A sprinter accelerates from rest to 9.00m/s in 1.38s. What is her acceleration in (a) m/s2 (b) km/h2 (2-19) A sports car moving at constant velocity travels 120m in 5.0s. If it then brakes and comes to a stop in 4.0s, what is the magnitude of its acceleration (assumed constant) in m/s2 , and in g’s (g = 9.80m/s2 )? (2-24) A light plane must reach a speed of 35m/s for takeoff. How long of a runway is needed if the (constant) acceleration is 3.0m/s2 (2-29) A car traveling at 95km/h strikes a tree. The front end of the car compresses and the driver comes to rest after traveling 0.80m. What was the magnitude of the average acceleration of the driver during the collision? Express the answer in terms of g’s, where 1.00g = 9.80m/s2 . (2-32) A driver is traveling 18.0m/s when she sees a red light ahead. Her car is capable of decelerating at a rate of 3.65m/s2 . If it takes her 0.350s to get the brakes on and she is 20.0m from the intersection when she sees the light, will she be able to stop in time? How far from the beginning of the intersection will she be, and in what direction? (2-33) A 75m long train begins uniform acceleration from rest. The front of the train has a speed of 18m/s when it passes a railway worker who is standing 180m from where the front of the train started. What will be the speed of the last car as it passes the worker? (See Figure 2-38 on page 44). (2-35) A runner hoes to complete the 10, 000m run in less than 30.0min. After running at a constant speed for exactly 27.0min, there is still 1200m to go. The runner must then accelerate at 0.20m/x2 for how many seconds in order to achieve the desired time? (2-40) Estimate (a) how long it took King Kong to fall straight down from the top of the Empire State Building (380m high), and (b) his velocity just before ”landing”. (2-42) A baseball is hit almost straight up into the air with a speed of 25m/s. Estimate (a) how high it goes, (b) how long it is in the air. As well, (c) what factors make this an estimate? (2-53) A falling stone takes 0.31 s to travel past a window 2.2 m tall. From what height above the top of the the window did the stone fall? Extra Credit–Optional: Choose One (2-48) A rocket rises vertically, from rest, with an acceleration of 3.2m/s2 until it runs out of fuel at an altitude of 775m. After this point, its acceleration is that of gravity, downward. (a)What is the velocity of the rocket when it runs out of fuel? (b) How long does it take to reach this point? (c) What maximum altitude does the rocket reach? (d) How much time (total) does it take to reach maximum altitude? (e) With what velocity does it strike the Earth? (f) How long (total) is it in the air? (2-62) A person jumps out a fourth-story window 18.0m above a firefighter’s safety net. The survivor stretches the net 1.0m before coming to rest (see Figure 2-45 on page 46). (a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net? (b) What would you do to make it ”safer” (that is, to generate a smaller deceleration); would you stiffen or loosen the net? Explain. Classwork #2 on Chapter 2 PHYS 2425 (2-9) A person jogs eight complete laps around a 400m track in a total time of 14.5min. Calculate (a) the average speed and (b) the average velocity, in m/s. (2.7) You are driving home from school steadily at 95km/h for 180km. It then begins to rain and you slow to 65km/h. You arrive home after driving 4.5h. (2-17) A sports car accelerates from rest to 95km/h in 4.3s. What is its average acceleration in m/s2 ? (2-21) A car moving in a straight line starts at x = 0 at t = 0. It passes the point x = 25.0m with a speed of 11.0m/s at t = 3.00s. It passes the point x = 385m with a speed of 45.0m/s at t = 20.0s. Find (a) the average velocity, and (b) the average acceleration, between t = 3.00s and t = 20.0s. (2-30) A car traveling 75km/h slows down at a constant 0.50m/s2 just by ”letting up on the gas”. Calculate (a) the distance the car coasts before it stops (b) the time it takes to stop (c) the distance it travels during the first and fifth seconds. (2-43) A kangaroo jumps straight up to a vertical height of 1.45m. How long was it in the air before returning to Earth? (2-49) A helicopter is ascending vertically with a speed of 5.40m/s. At a height of 105m above the Earth, a package is dropped from the helicopter. How much time does it take for the package to reach the ground? [Hint: What is v0 for the package?] (2-50) Roger sees water balloons fall past his window. He notices that each balloon strike the sidewalk 0.83s after passing his window. Roger’s room is on the third floor, 15m above the sidewalk. (a) How fast are the balloons traveling when they pass Roger’s window? (b) Assuming the balloons are being released from rest, from what floor are they being released? Each floor of the dorm is 5.0m high. (2-71) A stone is thrown vertically upward with a speed of 15.5m/s from the edge of a cliff 75.0m high (see Figure 2-48 on page 47) (a) How much later does it reach the bottom of the cliff? (b) What is its speed just before hitting? (c) What total distance did it travel?