Physics 150 Fall 2003

Solution to HW 1

1. Teleology refers to the principle of design in nature.  For example, a wing exists for the purpose of flying.    A nose exists to smell.  This may be opposed to the Darwinian view which posits that evolution slowly and often by chance changed various traits of organisms until wings or noses eventually developed.  Teleology would argue that those traits were designed.

2. An experiment is a method to collect data which can be used to test a hypothesis.

3. Richard Powers debates that Ibn al-Haytham’s resolution of the eight-hundred year old problem of how the eye sees is the most important idea of the millennium.  The actual discovery, that light enters the eye from observed objects and not the reverse, was important by itself.  More important, however, is the way he discovered this fact.  Rather than relying on reason and conjecture, as Ptolemy and Aristotle had done, or trusting authority, as the Western world was doing at that time period, Ibn al-Haytham simply looked.  He stared at the sun and realized that it hurt to do so, which suggests that light must emanate from objects since the brightness of objects would not change if the opposite were true.  His use of experimental data became the basis for modern scientific methods.

Another example of a debate that can be settled by experiment: does the Earth orbit around the sun or does the entire universe orbit the Earth.  Galileo resolved this debate using experimental data (observations of the heavens through a telescope) rather than by conjecture or reasoning alone.

4. Please note that you will need to show your work on future calculation problems.

A. A nail falls faster than a cardboard box due to the air resistance on the box.

2. a) for constant velocity: v = d/t = 100 m/10 s = 10 m/s.

b) still moving at constant velocity: t = d/v = 1610 m/10 m/s = 161 s.

4. for constant acceleration: a = (vf-vi)/(tf-ti) = (28 m/s – 22 m/s)/3 s = 2 m/s^2. (note the units on acceleration: meter per second squared)

10. a) the car stops at when vf=0.  for constant acceleration, t = (vf-vi)/a = (0 m/s – 30 m/s)/-6 m/s^2 = 5 s.

b) There are two ways of answering this question:

i) for constant acceleration: xf-xi = vi*t + 0.5*a*t^2 = 30*5 + 0,5*(-6 m/s^2)*5^2 = 75 m.

ii) The car decelerates uniformly, thus its average velocity is (vf-vi)/2 = 15 m/s.  Since it travels that average velocity for an interval of 5 s, the total distance traveled is 15 m/s * 5 s = 75 m.