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* BIO EST Water striders Water striders are insects that propel themselves on the surface of ponds by creating vortices in the water shed by their driving legs. The velocity- versus-time graph of a 17-mm-long water strider that moved in a straight line was created from a video (Figure P2.76). The insect started from rest, sped up by taking two strides, and then slowed down until it stopped. Estimate (a) the maximum speed (in m/s), (b) the maximum acceleration (in
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- (a) A world record was set for the men's 100-m dash in the 2008 Olympic Games in Beijing by Usain Bolt of Jamaica. Bolt "coasted" across the finish line with a time of 9.69 s. If we assume that Bolt accelerated for 3.00 s to reach his maximum speed, and maintained that speed for the rest of the race, calculate his maximum speed and his acceleration. (b) During the same Olympics, Bolt also set the world record in the 200-m dash with a time of 19.30 s. Using the same assumptions as for the 100-m dash, what was his maximum speed for this race?arrow_forwardA student drives a moped along a straight road as described by the velocity-versus-time graph in Figure P2.12. Sketch this graph in the middle of a sheet of graph paper. (a) Directly above your graph, sketch a graph of the position versus time, aligning the time coordinates of the two graphs. (b) Sketch a graph of the acceleration versus time directly below the velocity-versus-time graph, again aligning the time coordinates. On each graph, show the numerical values of x and ax for all points of inflection. (c) What is the acceleration at t = 6.00 s? (d) Find the position (relative to the starting point) at t = 6.00 s. (e) What is the mopeds final position at t = 9.00 s? Figure P2.12arrow_forwardA student drives a moped along a straight road as described by the velocitytime graph in Figure P2.32. Sketch this graph in the middle of a sheet of graph paper. (a) Directly above your graph, sketch a graph of the position versus time, aligning the time coordinates of the two graphs. (b) Sketch a graph of the acceleration versus time directly below the velocitytime graph, again aligning the time coordinates. On each graph, show the numerical values of x and ax for all points of inflection. (c) What is the acceleration at t = 6.00 s? (d) Find the position (relative to the starting point) at t = 6.00 s. (e) What is the mopeds final position at t = 9.00 s? Figure P2.32arrow_forward
- An object that moves in one dimension has the velocity-versus-time graph shown in Figure P2.52. At time t = 0, the object has position x = 0. a. At time t = 5 s. is the acceleration of the object positive, negative, or zero? Explain. b. At time t = 8 s, is the object speeding up, showing down, or moving with constant speed? Explain. c. Write an expression for the position of the object as a function of time. Explain how you use the graph to obtain your answer. d. Use your expression from part (c) to determine the time (if any) at which the object reaches its maximum position. Check your results by examining the graph. Hint: To get started with finding the maximum of a function, take the derivative and set it equal to zero.arrow_forwardA glider of length moves through a stationary photogate on an air track. A photogate (Fig. P2.19) is a device that measures the time interval td during which the glider blocks a beam of infrared light passing across the photogate. The ratio vd = /td is the average velocity of the glider over this part of its motion. Suppose the glider moves with constant acceleration. (a) Argue for or against the idea that vd is equal to the instantaneous velocity of the glider when it is halfway through the photogate in space. (b) Argue for or against the idea that vd is equal to the instantaneous velocity of the glider when it is halfway through the photogate in time. Figure P2.19arrow_forwardA speedboat travels in a straight line and increases in speed uniformly from i = 20.0 m/s to f = 30.0 m/s in displacement x of 200 m. We wish to find the time interval required for the boat to move through this displacement, (a) Draw a coordinate system for this situation, (b) What analysis model is most appropriate for describing this situation? (c) From the analysis model, what equation is most appropriate for finding the acceleration of the speedboat? (d) Solve the equation selected in part (c) symbolically for the boats acceleration in terms of i, f, and x. (e) Substitute numerical values lo obtain the acceleration numerically. (f) Find the time interval mentioned above.arrow_forward
- A glider of length moves through a stationary photogate on an air track. A photogate (Fig. P2.44) is a device that measures the time interval td during which the glider blocks a beam of infrared light passing across the photogate. The ratio vd = /td is the average velocity of the glider over this part of its motion. Suppose the glider moves with constant acceleration. (a) Argue for or against the idea that vd is equal to the instantaneous velocity of the glider when it is halfway through the photogate in space. (b) Argue for or against the idea that vd is equal to the instantaneous velocity of the glider when it is halfway through the photogate in time.arrow_forwardPROBLEM A race car starting from rest accelerates at a constant rate of 5.00 m/s2, (a) What is the velocity of the car after it has traveled 1.00 102 ft? (b) How much time has elapsed? (c) Calculate the average velocity two different ways. STRATEGY Weve read the problem, drawn the diagram in Figure 2.16, and chosen a coordinate system (steps 1 and 2). We'd like to find the velocity v after a certain known displacement x. The acceleration a is also known, as is the initial velocity v0 (step 3, labeling, is complete), so the third equation in Table 2.4 looks most useful for solving part (a). Given the velocity, the first equation in Table 2.4 can then be used to find the time in part (b). Part (c) requires substitution into Equations 2.2 and 2.7, respectively. Figure 2.16 (Example 2.4) SOLUTION (a) Convert units of x to SI, using the information in the inside front cover. Write the kinematics equation for v2 (step 4): Solve for v, taking the positive square root because the car moves to the right (step 5): Substitute v0 = 0, a = 5.00 m/s2, and x = 30.5 m: 1.00 102ft = (1.00 102 ft) v2 = v02 + 2a x v = v02+2ax v = v02+2ax = (0)2+2(5.00m/s2)(30.5m)= 17.5 m/s (b) Find the trooper's speed at that time. Substitute the time into the troopers velocity equation: vtrooper = v0 + atrooper t = 0 + (3.00m/s2)(16.9s) = 50.7 m/s Solve Example 2.5, Car Chase, by a graphical method. On the same graph, plot position versus time for the car and the trooper. From the intersection of the two curves, read the time at which the trooper overtakes the car.arrow_forwardA motorist drives for 35.0 minutes at 85.0 km/h and then stops for 15.0 minutes. He then continues north, traveling 130. Km in 2.00 h. (a) What is his total displacement? (b) What is his average velocity?arrow_forward
- There is a 250-m-high cliff at Half Dome in Yosemite National Park in California. Suppose a boulder breaks loose from the top of this cliff. (a) How fast will it be going when it strikes the ground? (b) Assuming a reaction time of 0.300 s, how long will a tourist at the bottom have to get out of the way after hearing the sound of the rock breaking loose (neglecting the height of the tourist, which would become negligible anyway if hit)? The speed of sound is 335 m/s on this day.arrow_forwardThe Acela is an electric train on the Washington-New YorkBoston run, carrying passengers at 170 mi/h. A velocity-time graph for the Acela is shown in Figure P2.69. (a) Describe the train's motion in each successive lime interval, (b) Find the trains peak positive acceleration in the motion graphed, (c) Find the trains displacement in miles between t = 0 and t = 200 s.arrow_forwardAn object is at x = 0 at t = 0 and moves along the x axis according to the velocitytime graph in Figure P2.40. (a) What is the objects acceleration between 0 and 4.0 s? (b) What is the objects acceleration between 4.0 s and 9.0 s? (c) What is the objects acceleration between 13.0 s and 18.0 s? (d) At what time(s) is the object moving with the lowest speed? (e) At what time is the object farthest from x = 0? (f) What is the final position x of the object at t = 18.0 s? (g) Through what total distance has the object moved between t = 0 and t = 18.0 s? Figure P2.40arrow_forward
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