# 2011 Semester 1 Physics Final

**Physics Semester I Final2016**

STUDY GUIDE

ANSWERS

- What are the seven main branches of physics? What do they study?
- Mechanics, Thermodynamics, Vibrations and wave phenomena, Optics, Electromagnetism, Relativity, Quantum mechanics
- What are the SI base (fundamental) units for length, mass, and time?
- meter, kilogram, second
- Write the following numbers in scientific notation:

a. 450000 b. 39c.0.000821d. 110020e. 0.0000004800

- 4.5 x 105
- 3.9 x 101
- 8.21 x 10-4
- 1.10020 x 105
- 4.800 x 10-7

- Calculate the following (sig fig rules):
- (300)(250) = 80 000
- 3.0 + 2.0 = 5.0
- 3.0 – 1 = 2
- 2.00 + 1.000+ 3 = 6
- 1.0 x 12 = 12
- (1)(1200) = 1000
- 2.00 ÷ 35 = 0.057

5.If your next class is 300 yards away, how long will it take you to get there walking at a constant speed of 3 ft/s?

- v=x/t, so t=x/v, but we need to convert yards to feet, so t = 900/3 = 300s.

6.You drop a penny from the top of the bleachers which is 5 m tall. If it hits the ground 1 s later, what is the penny’s average speed as it falls?

- asks for average speed so v=x/t = 5/1 = 5m/s

7.Sketch a distance vs time graph for an object moving at constant speed.

- speed is equal to the slope of the line on a distance v time graph, so we should see a graph of a straight line

8.What is the difference between a scalar and a vector?

- scalar has magnitude; vector has magnitude and direction

9.

Using the vectors above, do the following vector additions showing the resultant vector, approximate the vector’s magnitude as you draw them (DO NOT DO ANY CALCULATIONS!):

a. A + Bb. C + Dc. C + E d. G – Ee. H + E

10.What is a projectile? What is the general shape of a projectile’s path?

- projectile = falling object with horizontal velocity; parabola

11.What is true about the horizontal & vertical velocity of a projectile? In what circumstance/s can the vertical velocity of a projectile be zero?

- horiz. velocity is constant; when rolling on flat surface or at top of flight

12.While following the directions on a treasure map, a pirate walks 45.0 m north, then turns and walks 15 m west. What is the magnitude of the pirate’s displacement?

13.A pelican flying along a horizontal path drops a fish from a height of 5.4 m. The fish travels 8.0 m horizontally before it hits the water below. What is the pelican’s speed?

y-dirx-dir

14.An autographed baseball rolls off of a 0.70 m high desk with a velocity of 0.66 m/s. How far away from the base of the desk does the baseball hit?

- y-dirx-dir

15.Mr. Miles and Mr. Garcia are playing tug-of-war. If Mr. Garcia applies a force of 1000 N to the left and Mr. Miles applies a force of 800 N to the right, what additional force is needed to produce equilibrium?

- 200N, to the right

16.What force must be applied to keep a 50 kg cheerleader up in the air?

- The force required to hold something up is equal to the weight of the object, and W = mg = 50*9.8 = 490N

17.Sketch a velocity vs time graph for a moving object if all the forces on the object are balanced.

- If all the forces are balanced, there is no net force and no acceleration. On a velocity v time graph, the acceleration is the slope of the line and since there is no acceleration, the line should have a slope of zero, which would be a horizontal line

18.A 75 kg water skier is holding a rope that has a tension of 500 N. If the water provides a resistance force of 50 N, what is the skier’s acceleration?

- The net force = 500N – 50N = 450N. The net force also equals mass times acceleration or a = F/m = 450N/75kg = 6m/s2

19.You apply a 200 N force to a 25 kg piece of furniture. What will its acceleration be?

- F=ma or a = F/m = 200N/25kg = 8m/s2

20.You apply 40 N of force to a 10 g nail by hitting it with a hammer. What is the force of the nail on the hammer?

- Newton’s 3rd, for every action there is an equal and opposite reaction, 40N

21.If you stand on a scale and then jump up, how would the reading on the scale change?

- Newton’s 3rd again, a force is required to push you up. it’s the reaction to you pushing down on the scale. Since you’re pushing down the scale will momentarily read higher

22. How would the gravitational force between the Earth and the moon change if…

- F=Gm1m2/r2

- the mass of the Earth was doubled?
- force would be double
- the distance between the centers of the Earth and Moon was doubled?
- force would be one forth
- the mass of the moon was halved?
- force would be one half
- the distance between the centers of the Earth and Moon was halved?
- force would be four times as much

23.Why is the force of gravity so much larger on the Earth than it is on the moon?

- The mass of the earth is very large compared to the moon

24.What force causes the Moon to move around the Earth?

- Gravity

25.Which direction does the force on the Moon point?

- towards center of the earth

26.Which direction will the following object go if the force causing to move in a circle suddenly disappeared?

- directly up, in a straight line, tangent to the circle

27.As car is turns a corner, what force keeps the car from skidding? Which way is it directed?

- friction, towards the center of the turn

28.What will happen to the car if it hits a patch of ice?

- friction will disappear and car will travel in a straight line, tangent to the circle

29.What is the kinetic energy of a 2000 kg car moving at 30 m/s?

- KE=1/2mv2 = ½*2000*302 = 900000 J

30.A large vase is dropped and breaks into 5 different pieces, each travelling with a speed of 2 m/s after shattering. If the pieces weigh 1 kg, 2 kg, 3 kg, 4 kg, and 5 kg, respectively, what is the total kinetic energy of all the pieces after shattering?

- Add all KE together: ½*1*22 + ½*2*22 + ½*3*22 + ½*4*22 + ½*5*22 = 30J

31.What is the kinetic energy of a 5 kg rock thrown at 8.0 m/s?

- KE = ½*5*82 =160J

32.What is the kinetic energy of a 0.15 kg baseball travelling 50 m/s?

- KE = ½*.15*502 =190J

33.A 15 kg monkey is in a tree 15 meters off the ground. If the monkey climbs down 10 m, how much did its potential energy decrease by?

- change in PE = PEf - PEi = mghf – mghi = 15*9.8*5 – 15*9.8*15 = -1470, so decrease of 1500J

34.You lift a 50 kg barbell over your head to a height of 2 m. What is its potential energy?

- PE=mgh = 50*9.8*2 = 980J

35.You drive your 1500 kg car to the top of a 15 m parking structure. How much has its potential energy increased by?

- PE=mgh = 1500*9.8*15 = 220000J

36.You leave your car running and in gear as you get out and the car drives itself off of the parking structure. What form of energy will increase? Decrease?

- Kinetic energy will increase as the car falls but potential energy will decrease

37.What will be the car’s kinetic energy just before hitting the ground?

- conservation of energy: PEi + KEi = PEf + KEf
- Let’s assume the car rolled off at negligible speed so initial KE =0
- 220000 + 0 = 0 + KEf, so KEf = 220000J

38.Starting from rest, a 20-kilogram block slides a distance of five meters down a frictionless slope, as shown.

What is the approximate kinetic energy of the wooden block at the bottom of the slope?

- conservation of energy: PEi + KEi = PEf + KEf
- mgh + 0 = 0 + KEf
- 20*9.8*3 = KEf = 590J

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