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#### Physics

Physics Questions and Answers (Question is listed first; Answer is the latter, with corresponding number)

# Ch 2

1. An object moving in a straight line can be described by what type of motion? 1.

1. Translational is straight, non-rotating movement

2.  Although often used interchangeably in every-day language, what is the difference between speed and velocity?

2. Velocity is a vector, i.e., it is a magnitude with direction; speed is a scalar, only a magnitude.

3. A cyclist rides 30 km North, and then 40km East.  The time of the ride was 1.5 hours.  What was the average velocity in (km/h)?  What was the average speed (in km/h)?

3. 33.3km/h; 46.7 km/h

4. An airplane travels in a straight line from city A to city B in 3 hours 45 min.  The airplane’s speed was constant at 800 km/h.  How far is it from A to B (in km)?

4. 3000 km

5.  What is acceleration?  Describe units of measurement for acceleration?

5. Change in velocity in units of distance per (unit time)2

6. Cheetah’s can run from zero to about 60 km/hour (40 mph) within 2 seconds when chasing their prey.  What is the cheetah’s average acceleration during this time (in m/s2)?

6. 8.33 m/s2

7. A cyclist peddling in the Tour de France on a flat road and sees a wreck just ahead, at point B.  As he hits the brakes at point A he is traveling 50 km/h.  It takes him 3 seconds to slow to 10 km/h by point B.  What was the magnitude of his acceleration (m/s2) from A to B?  In which direction is does the acceleration point compared to the velocity?

7. 3.7 m/s2 opposite direction to velocity (10-50)

8. A bullet is fired rifle with a 1.1 m barrel.  The bullet emerges from the barrel .004 seconds after it is fired from rest.  Assuming constant acceleration, how fast (m/s) was the bullet traveling as it left the barrel.

8.  550 m/s

9. A young alien (on another planet) standing on a bridge 30 m high drops a rock into a stream below.  It took 2.4 seconds to hit the water after letting the rock go from rest.  What is the acceleration of that planet’s gravity, assuming no air resistance and constant acceleration of the rock?  How does this value compare to earth’s acceleration of gravity (9.8 m/s2)?

9. 10.42, greater than earth.

10.  An alien measures the height of a cliff by dropping a boulder from rest and measuring the time it takes to hit the ground below.  The boulder fell for 23 seconds on a planet with an acceleration of gravity of 7.9 m/s2.  Assuming constant acceleration and ignoring air resistance, how high was the cliff?

2090 m high

11. A pitcher throws a baseball straight with a velocity of 160 km/h to his catcher.  The ball had an acceleration of 30 m/s2.  How far away was the catcher?

11. 33m

12. A parachuter plans to pull his parachute after falling 6000 feet.  He falls with a constant acceleration of 9.8 m/s2.  How long (in minutes) should he wait in free-fall before pulling his chute?

12. .32 min

13.  A parachuter’s friend pushes him down from an airplane with an initial velocity of 2 m/s.  He falls with an acceleration of 9.8 m/s2.  How far did he fall after 10 seconds?

13. 510 m

14. A small artillery shell is fired straight up into the air with an initial velocity of 300 m/s.  After traveling up, gravity eventually stops the shell briefly (velocity is zero) before it falls back down.  How high does the bullet go?  Approximately how long is it in the air?

14.  4591 m; 1 minute

15. The distance a car travels (in meters) is measured vs. time (sec).  A plot of data gives an average slope of 17.5.  What is the magnitude of the velocity during the time interval from 10 to 17 seconds?

15. 17.5 m/s

16. A rescue plane wants to drop provisions on a target.  The plane flies at 50 m/s and is at a constant elevation above the target.  Upon release of provisions, the angle (above the horizontal) between the approaching plane and it’s target is 55 degrees.  The plane is still 1000 m away (horizontally) from the target.  How high is the plane?

# 16.  1428 m high

17.  True or False
Objects in falling through the air on earth will continuously increase in velocity, since the acceleration of gravity is constant at 9.8 m/s2
17. False - Terminal velocity.  Objects slow down due to air resistance etc
18. A rabbit is startled by a fox runs away.  From rest, the rabbit accelerates at a constant rate of 11 m/s2.  At this rate how far away could the rabbit be after 6 seconds?
18. 198 m
19. A police car traveling 10 m/s sees a speeding car and races to catch it.  Assuming a constant acceleration of the police car of 6 m/s2, how fast in miles per hour will the police car be traveling if it catches the offending car 250 m ahead? (There are 5280 feet per mile and 2.54 cm per inch)
19. 125 mph

# Chapter 3

20.  One tennis ball is dropped from the side of a 2 story building.  At exactly the same time, another identical tennis ball is thrown horizontally from the same height.  Which ball hits the ground first?

20. Both hit at the same time since vertical components are the same.  The thrown ball travels further horizontally in the time interval, however.

21.  A golf ball and a heavy bowling ball are both dropped from a height of 200m.  Which hits the ground first?

21. They hit at the same time according to Galileos experiment

22.   A boy traveling in a car at 40 km/h throws an egg out the window in the same direction as the car is traveling.  The boy throws the egg with a velocity of 8 m/s.  How fast (m/s) does the egg travel according to a man standing on the street. How fast (m/s) does the egg move according to the boy?

22. 19 m/s; 8m/s

23. A baseball pitcher throws a ball with a velocity (relative to the pitcher) of 30 m/s from the back of a pick-up truck traveling 20 m/s in the opposite direction of the ball.  How fast was the ball traveling according to the catcher, standing on the road?

23. 10 m/s

24. A water balloon is launched horizontally from a height of 30 m.  The target is 100 m away in the horizontal direction.  How long will the balloon be in the air (neglecting air resistance, assuming constant acceleration)?  With what velocity must it be launched in order to hit the target?

24.  2.5 s;  40m/s

25.  A water balloon is dropped from rest from a height of 30m.  How long before it hits the ground (neglecting air resistance, assuming constant acceleration)?

25. 2.5 s

26.  A man throws a rock at a 60 degree angle with the horizontal at an initial velocity of 10 m/s.  How high does the rock go?

26.  5.84 m

27.  What is the total time in the air for a rock thrown at a 60 degree angle and initial velocity 10 m/s?
27. 2.18 s

28.  A man wants to throw a rock across a river.  The distance across is 25 m.  He throws the rock with an initial velocity of 10 m/s at a 60 degree angle from the horizontal.  How far does the rock travel?  Does it make it across the river?

28. 10.9 m; no

29.  A baseball player hits a fly-ball to a height of 25 m with an initial velocity of 17 m/s at an angle of 80 degrees with the horizontal.  How long do the fielders have to catch the ball before it hits the ground from the time the ball was hit?

29. 3.4 s

30. The time for a cannon ball launched with an initial velocity of 40 m/s at an angle of 45 degrees with the horizontal to reach its max height is 2.89 s.  How high does the ball go?

30. 40 m

31.  The time for a cannon ball launched with an initial velocity of 40 m/s at an angle of 45 degrees with the horizontal to reach its maximum height is 2.89 sec.  What is the total time the ball is in the air? How far does the ball go?

31. 5.78 s; 162 m

32.  A trick-biker wants to jump over a 2.5 m tall car.  He leaves a ramp with a velocity of 10 m/s.  The ramp is at a 20 degree angle with the horizontal.  Does the biker get high enough?

32. .59 m, no

33.  If a biker leaves a ramp (20 degrees with the horizontal) at 10 m/s, can he jump over a ditch 5 m wide?  How much over or under 5 m is the biker?

33. yes, he has roughly 1.5 m to spare.

34.  What type of path does any projectile particle follow, assuming no air resistance and constant gravitational acceleration?

34. parabolic path

35. What are the three Newtons Laws of motion?

35. 1. an object will continue in motion or at rest unless a net force acts upon it.  2. F=ma. 3. Whenever one object exerts a force on a second object, the second exerts an equal force in the opposite direction on the first.
Chapter 4
36. A buffalo lying on the ground on earth weighs 1.5 tons (1 ton = 2000 lbs.  2.2 lb = 1 kg).  What force (in Newtons) is it exerting on the ground (assuming weight distribution is equal and gravitational acceleration is constant)?
36. 13363 N
37. Two piano movers push on a 250 kg piano on a frictionless surface.  What is the magnitude of force they must exert to move the piano horizontally?
37. 2450 N
38. Two forces act on an 8 kg block.  One force is 5N in the horizontal direction (to the right).  The other is 11N at an angle of 45 degrees with the horizontal (pointing in the positive direction of both the x and y axes).  Assuming these are the only forces present, what are the horizontal and vertical components of the acceleration of the block?
38. 1.6 horizontal, .97 vertical
39.  Two blocks are pulled along a frictionless surface.  Block 1 weighs 3 kg and block two weighs 2 kg.  Block 1 is attached to block 2 by Rope 1.  Block 2 also has another rope, Rope 2, which is used for pulling both the blocks together.  Both ropes are horizontal.  The blocks are moved at a constant acceleration of 2 m/s2.  Assume the ropes do not have mass.  What are the tensions on Rope 1 and Rope 2?
39. Rope 1 = 6 N; Rope 2 = 10 N
40. Three girls pull horizontally on a tire.  Girl A pulls with a force of 100 N north.  Girl B pulls with a force of 146 N at an south.  Girl C pulls with a force of 60 N at an angle of 45 degrees between north and east (in the positive x and y direction if north-south is y and x is east-west).  In which direction does the tire move?
40. south (3.6 N force)
41. What is inertia?  It is associated with which of Newton’s Laws?
41. The tendency of an object to maintain its state of rest or of uniform motion in a straight line.  Newton’s first law.
42.  What is the difference between mass and weight?  Which changes on the moon compared to earth?
42. Mass is a measure of an object’s inertia, i.e. how much matter it has.  Weight is a force, i.e., the pull of gravity on an object.  Mass stays the same everywhere.
43.  A cyclist must stop her bike in 10 m.  She is traveling at a velocity of 17 m/s.  The combined mass of the cyclist and bicycle is 80 kg.  What is the force required to stop the bike in this distance?
43. -1156 N
44.  On earth, a man has a mass of 67 kg.  What is his weight on a planet with a gravitational acceleration 75% that of earth’s (9.8 m/s2).  What is his mass on that planet?
44. 492 N.  67 kg.
45. A large piece of pipe (900 kg) is attached to the cable of a construction crane.  What is the tension of the cable when the crane lifts the pipe?
45.  8820 N
46. A 5 kg block sits on a ramp whose incline is 40 degrees with the horizontal ground.  What is the magnitude of the normal force?
46. 37.5 N
47. A large 45 kg package rests on the smooth ramp of a delivery truck.  The ramp makes a 33 degree angle with the horizontal.  If the coefficient of static friction between the ramp and the box is ms =  .9, what is the magnitude of the force of friction keeping the box at rest?
47.  240 N
48. A 70 kg snow skier is stopped on a hill 60 degrees with the horizontal.  What must the coefficient of static friction be between the skier and the snow?
48. 1.73
49. An airplane planning to fly directly west at 500 miles/hour is bombarded by a constant tail wind at 20 m/s blowing directly south to north, blowing the plane off course.  What is the resultant angle of deviation off course?
49.  5.13 degrees to the northwest
50. An airplane planning to fly directly west at 220 m/s is bombarded by a constant tail wind at 30 m/s blowing directly south to north, blowing the plane off course.  To what angle should the pilot direct the plane, in order to continue directly on course?
50. Aim 7.8 degrees to the southwest

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