Chapter 2, Problem 68P

We are standing on the top of a 720 feet tall building and launch a small object upward. The object's height, measured in feet, after t seconds is h(t) = - 16t2 +64t+ 720. = A) What is the object initial velocity? B) What is the highest point that the object reaches? ft/second feet

A student holds a ball 1.55 meters above the ground and drops it. Her friend uses a stopwatch and measures a time of 0.57 seconds for the ball to hit the ground. The ball accelerates due to gravity. Using the equation y = 1/2??2  where y is the height, to compute g , calculate the acceleration of the ball.

Maria throws two stones from the top edge of a building with a speed of 2.9 x 10' m/s. The height of the building is 7 x 102 meters. She throws one straight down and the other straight up. The first one hits the street in a time tj. How much later is it before the second stone hits? answer in seconds.

My question isn't how to solve the problem exactly.  In fact, it's already been solved on this website.  My question is about the acceleration.  When I solve this problem myself, first I calculate the velocity by dividing 100m by 53s.  I get 1.89m/s.  Then I use that to find the acceleration using the equation vf = vi + at.  That's 1.89/53 = 0.036m/s^2. That's not correct.  The correct way to find the acceleration is to us the equation d = 1/2 at^2 and solve that way without taking the intermediate step of finding the velocity.  Doing it that way, the acceleration is 0.0712m/s^2.  My question is why you get a different result doing it the first way than you get doing it the second way.

An object moves in one dimensional motion with constant acceleration a = 4.5 m/s². At time t = 0 s, the object is at xo = 2.9 m and has an initial velocity of vo = 4 m/s. How far will the object move before it achieves a velocity of v = 7 m/s? Your answer should be accurate to the nearest 0.1 m.

A thief is trying to escape from a parking garage after completing a robbery, and the thief’s car is speeding (v = 11 m/s) toward the door of the parking garage (Fig. P2.60). When the thief is L = 14 m from the door a police officer flips a switch to close the garage door. The door starts at a height of 7 m and moves downward at 0.3 m/s. If the thief’s car is 1.4 m tall, will the thief escape? (Find the height of the door above the ground).

A test rocket is fired vertically upward from a well. A catapult gives it initial speed 60 m/s at ground level. Its engines then fire and it accelerates upward at 5.0 m/s² until it reaches an altitude of 1,100 m. At that point its engines fail and the rocket goes into free-fall, with an acceleration of g=9.80 m/s². What is its velocity just before it collides with the Earth? (You will need to consider the motion while the engine is operating separately from the free-fall motion.) [Give your answer in m/s to the nearest 0.1 m/s]

An object has a velocity of (5.4 m/s)i -(4.8 m/s)j. Over a period of 1.3 s, its velocity changes to (1.7 m/s)i + (5.9 m/s)j. What is its acceleration? Group of answer choices   a) -(3.7 m/s)i +(11 m/s)j b) -(2.8 m/s)i+(8.2 m/s)j c) (3.7 m/s)i+(11m/s)j d) (2.8 m/s)i+(8.2 m/s)j e) -(2.8 m/s)i+(1.1 m/s)j

A jet plane comes in for a landing with a speed of 120 m/s. The length of the runway is 500 m. From the instant the plane touches the runway,   what is the magnitude of the acceleration needed to stop within the runway? Write your answer in terms of m/s2.