A cannon on a flat railroad car travels to the east with its barrel tilted 30 above horizontal. It fires a cannonball at 50 m/s. At t = 0 s, the car, starting from rest, begins to accelerate to the east at 2.0 m/sz. V Part A At what time should the cannon be fired to hit a target on the tracks that is 400 m to the east of the car's initial position? Assume that the cannonball is fired from ground level. Express your answer with the appropriate units. t : Previous Answers Quest Answer X Incorrect; Try Again; 5 attempts remaining Learning Goal: To practice Tactics Box 4.1 Finding the Acceleration Review Vector. Suppose an object has an initial velocity vi at time Below is another motion diagram for an object that moves along a curved path. The dots ti and later, at time to , has velocity of . The fact that represent the position of the object at five subsequent instants, t1, t2, t3, t4, and t5. The the velocity changes tells us that the object vectors U21, 132, 143, and v54 represent the average velocity of the object during the four undergoes an acceleration during the time interval corresponding time intervals. Draw the acceleration vectors a31 and a53 representing the At = tf - ti. From the definition of acceleration, changes in velocity of the object during the time intervals At31 = t3 - t1 and At53 = t5 - t3, respectively. a = of - vi Av If - ti At " Draw the vectors starting at the appropriate black dots. The location, orientation, and we see that the acceleration vector points in the length of the vectors will be graded. same direction as the vector Av. This vector is the change in the velocity Av = of - vi, so to know which way the acceleration vector points, we have to perform the vector subtraction of - vi. This Tactics Box shows how to use vector subtraction to find the acceleration vector. No elements selected Figure