Homework Help: Motion

Odd # Problems p 47-8

1. average speed = distance traveled/elapsed time
3. A tail wind is one that pushes you in the direction you are going. We are adding two velocity vectors in the same direction. Remember this question requires a magnitude and a direction, since it is a velocity.
5. Here we have two velocity vectors at right angles. (a) Find the resultant vector magnitude with Pythagorean theorem and the direction using the proper trig function. ( 13 m/s @ 16 degrees from straight across) (b) Remember the width of the river is measured directly across; to calculate the time, use the velocity component in the same direction as the measurement. (110 s) (c) Using the time from part b, how far will the boat drift downstream in that much time?(380 m)
7. Another right angle vector problem, but harder than #5. In order to end up going straight across, the swimmer must head slightly upstream. The result will be a slightly slower speed than he could manage in still water. (a) Set up a triangle with the swimmer's speed as the hypotenuse and the current as the opposite side of the heading angle. (b) Right triangle geometry.

Even # Problems p 56

2. Typical constant acceleration problem: Take given information, find equation that relates the quantities, solve for the unknown, substitute the given values for the proper symbols, do the math. Double check by analyzing the units. (a) given a and t , asked to find d, initial velocity is 0. (93 m) (b) Now initial velocity is 4.0 m/s; use equation form that includes initial velocity term. (120 m)
4. Free fall problem, use g for the acceleration. (a) Given d, asked to find final speed. Initial speed is zero. (b) Same situation, now find t.
6. Another typical constant acceleration problem. (a) Initial speed = 0. Solve for final speed with given acceleration and distance. (b) Same situation, now find t.
8. A two part problem, and fairly tricky. In the first part we have upward acceleration starting from rest and resulting in an upward final velocity. Then in the second part, this upward velocity becomes the initial velocity for a free fall problem. In the free fall situation, the acceleration is g, directed downward, causing the upward velocity to decrease to zero at which time maximum height is reached and the rocket begins to fall. Find the distance traveled in the first situation using constant acceleration equation. Now find distance rocket travels before v = 0 using free fall equation.