25 January 2013

Physics Homework Ch2

1. Light travels at a speed of about 3.0 X  m/s.
(a) How many miles does a pulse of light travel in a time interval of 0.1 s, which is about the blink of an eye?
(b) Compare this distance to the diameter of Earth. (Use 6.38 X 106 m for the radius of the Earth.)

VIDEO Answer:



2. a person travels by car from one city to another with different constant speeds between pairs of cities. She drives for 60.0 miin at 70.0 km/h, 11.0 min at 90.0 km/h, and 35.0 min at 35.0 km/h and spends 20.0 min eating lunch and buying gas
(a) Determine the average speed for the trip (km/h)
(b) Determine the distance between the initial and final cities along the route

VIDEO Answer:




3. Two boats start together and race across a 72-km-wide lake and back. Boat A goes across at 72 km/h and returns at 72 km/h. Boat B goes across at 36 km/h, and its crew, realizing how far behind it is getting, returns at 108 km/h. Turnaround times are negligible, and the boat that completes the round-trip first wins.
(a) Which boat wins? (or is it a tie)?
-- By how much?
(b) What is the average velocity of the winning boat?



4. A graph of position versus time for a certain particle moving along the x-axis is shown in the figure below. Find the average velocity in the following time intervals:

Graph of Position Versus Time











(a) 0 to 2.00 s
(b) 0 to 4.00 s
(c) 2.00 to 4.00 s
(d) 4.00 to 7.00 s
(e) 0 to 8.00 s




5. Two cars travel in the same direction along a straight highway, one at a constant speed of 55 m/h and the other at 65 mi/h.
(a) Assuming they start at the same point, how much sooner does the faster car arrive at a destination 7 mi away?
(b) How far must the faster car travel before it has a 15-min lead on the slower car?




6. The cheetah can reach a top speed of 114 km/h (71 mi/h). While chasing its prey in a short sprint, a cheetah starts from rest and runs 48 m in a straight line, reaching a final speed of 76 km/h
(a) Determine the cheetah's average acceleration during the short sprint
(b) Find its displacement at t = 3.3 s. (Assume the cheetah maintains a constant acceleration throughout the sprint).




7. A car traveling east at 45.1 m/s passes a trooper hiding at the roadside. The driver uniformly reduces his speed to 25.0 m/s in 3.80 s.
(a) What is the magnitude and direction of the Car's acceleration as it slows down?
  - Magnitude is m/s^2
(b) How far does the car travel in the 3.80-s time period?




8. The velocity vs. time graph for an object moving along a straight path is shown in the figure below.
Graph of Velocity versus Time














(i) find the average acceleration of this object during the following time intervals.
0s to 5.0 s (m/s^2)
5.0 s to 15 s (m/s^2)
0 s to 20 s (m/s^2)

(ii) Find the instantaneous accelerations at the following times
2.0 s (m/s^2)
10 s (m/s^2)
18 s (m/s^2)




9. A steam catapult launches a jet aircraft from the aircraft carrier John C. Stennis, giving it a speed of 170 mi/h in 2.6 s
(a) Find the average acceleration of the plane (m/s^2)
(b) Assuming the acceleration is constant, find the distance the plane moves (m)




10. An object moving with uniform acceleration has a velocity of 11.0 cm/s in the positive x-direction when its x-coordinate is 2.97 cm. If its x-coordinate 1.85 s later is -5.00cm, what is its acceleration? (cm/s^2)



11. A truck covers 40.0 m in 7.05 s while uniformly slowing down to a final velocity of 2.25 m/s.
(a) Find the truck's original speed (m/s)
(b) find its acceleration (m/s^2)



12. A Cessna Aircraft has a liftoff speed of 120 km/h.
(a) What minimum constant acceleration does the aircraft require if it is to be airborne after a takeoff run of 270 m (m/s^2)?
(b) How long does it take the aircraft to become airborne (seconds)?





13. A jet plane lands with a speed of 118 m/s and can accelerate at a maximum rate of -5.20 m/s^2 as it comes to rest.
(a) From the instant the plane touches the runway, what is the minimum time needed before it can come to rest (seconds)
(b) Can this plane land on a small tropical island airport where the runway is 0.800km long?



14. A car starts from rest and travels for 9.0 s with a uniform acceleration of +1.9 m/s^2. The driver then applies the brakes, causing a uniform acceleratoin of -1.0 m/s^2. If the brakes are applied for 3.0 s, determine each of the following.
(a) How fast is the car going at the end of the braking period (m/s)?
(b) how far has the car gone (m)?





15. A ball is thrown vertically upward with a speed of 10.0 m/s.
(a) How high does it rise (m)?
(b) How long does it take to reach its highest point (s)?
(c) How long does the ball take to hit the ground after it reaches the highest point (s)?
(d) What is its velocity when it returns to the level from which it started?



16. A ball is thrown directly downward with an initial speed of 8.20 m/s, from a height of 29.8 m. After what time interval does it strike the ground (s)




17. A baseball is hit so that it travels straight upward after being struck by the bat. A fan observes that it takes 2.90 s for the ball to reach its maximum height.
(a) Find the ball's initial velocity (m/s)
(b) Find the height it reaches (m)

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