College Physics

Bob has just finished climbing a sheer cliff above a beach, and wants to figure out how high he climbed. All he has to use, however, is a baseball, a stopwatch, and a friend on the ground below with a long measuring tape. Bob is a pitcher, and knows that the fastest he can throw the ball is 76.0 mph. bob starts the stopwatch as he throws the ball (with no way to measure the ball's initial trajectory), and watches carefully. The ball rises and then falls, and after 0.176 seconds the ball is once again level with Bob. He can't see well enough to time when the ball hits the ground. Bob's friend then measures that the ball landed 431 ft from the base of the cliff. How high up is Bob, if the ball started from exactly 5 ft above the edge of the cliff?

Answers

Bob is about 157.64 feet up the cliff. Since we know the ball travels at 76.0 mph (34.39 m/s) we can use the equation for uniform acceleration: vf^2 = vi^2 + (2*a*d) where vf is the final velocity of the ball, vi is the initial velocity of the ball (zero, since it is being thrown), a is the acceleration of gravity (9.8 m/s^2), and d is the distance the ball has traveled. We can use this equation to determine the y-component of the initial velocity (vy) of the ball, which is the component that helps the ball travel upwards out of the initial five feet of the cliff's edge. vy = sqrt(2*a*d) = sqrt(2*9.8*5) = 14.14 m/s Since the ball travels upwards at a constant speed of 14.14 m/s and then follows a curved path downwards for 0.176 seconds, we can calculate the total distance traveled by the ball: Distance traveled = (vy * time) + 1/2(acceleration of gravity * time^2) Distance traveled = (14.14 m/s * 0.176 s) + 1/2(9.8 m/s^2 * 0.176 s^2)

Answered by regina21

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