**THE SECOND HOUR EXAM **

NATURAL SCIENCE 105

SECOND HOUR EXAM
Do all your writing in your blue book(s) making sure your name is on each blue book you use. Each question is worth the value indicated in
parentheses. Be sure to show your work for all computations and give explanations where they are requested. For all questions, you may set the value
of g equal to 10 m/s/s/.

1. State each of Newton.s 3 laws of motion. (10)

2.

a) What is the weight (on earth) of a mass of 100kg? (5)

b) What would the weight of this mass be on a planet where the value of g is 25 m/s/s? (5)

3. After she jumps, a sky diver reaches terminal velocity in ten seconds. Does she gain more speed during the first second of fall or the ninth
second of fall? Compared with the first second of fall, does she fall a greater or lesser distance during the ninth second? (10) (You cannot neglect
air friction in this question).

4.

a ) A horizontal force of 100 N is required to push a crate across a horizontal factory floor at constant speed. What is the net force acting
on the crate? What is the force of friction acting on the crate? (10)

b. If the mass of the crate is 30 kg, what is the coefficient of friction between the crate and floor? (5)

5. In the 1920s, the New York Times published an editorial (later retracted) that ridiculed Robert Goddard for proposing space flight. The
editorial argued that space flight was clearly ridiculous since the rocket would have nothing to push against once it left the earth.s atmosphere.
What force propels a rocket when it is in space? (10)

6. Define each of the following terms: impulse, momentum, Law of Conservation of Momentum. (10)

7. Imagine a steel bullet and a rubber bullet, each of exactly the same mass, being fired from a gun at exactly the same speed. If they are each
fired at identical soda cans, the steel bullet will rip through the soda can and continue on its journey, the rubber bullet will bounce off the can.
In which collision (i.e., steel bullet/can or rubber bullet/can) was there more forced exerted on the can by the bullet? Explain your reasoning. (10)

8.

a) Consider a mass of m resting on the edge of a building a height h above the ground. What is its potential energy atop the building? Its
kinetic energy? (5)

b) If it is released from rest and falls to the earth, what is its kinetic energy just before impact? What is its potential energy at that point? (5)

c) If h has a value of 5 m, what is the speed with which the object hits the ground? Show your work. (5)

9.

a) How much work would be required to lift an object of 100 kg to a height of 30 m (roughly the height of Damen Hall)? (5)

b) Suppose you raised the object to this height by sliding it up an inclined plane of total ramp length 90 m. Assuming no friction between the ramp
and object, how much force would be required to push this object along this ramp? Explain your reasoning and/or show your work. (10)