# Problem Set 1 General Physics

FEU ALABANG

Senior High School Program

Problem Set 1 in General Physics

Topic(s) Number of Items Total Points Submission Date

Measurement and Motion in Straight Line 15 100 After 8 days

1. A certain compact disc (CD) contains 783.216 megabytes of digital information. Each byte consists of exactly 8 bits. When played, a CD player reads the CD’s information at a constant rate of 1.4 megabits per second. How many minutes does it take the player to read the entire CD?

2. While driving in an exotic foreign land you see a speed limit sign on a highway that reads 180,000 furlongs per fortnight. How many miles per hour is this?(One furlong is 1/8 mile, and a fortnight is 14 days. A furlong originally referred to the length of a plowed furrow.)

3. Can the velocity of an object be negative when its acceleration is positive? What about vice versa? If yes, give examples in each case.

4. You travel from point A to point B in a car moving at a constant speed of 70 km/h. Then you travel the same distance from point B to another point C, moving at a constant speed of 90 km/h. Is your average speed for the entire trip from A to C equal to 80 km/h? Explain why or why not.

5. Starting from the front door of your ranch house, you walk 60.0 m due east to your windmill, and then you turn around and slowly walk 40.0 m west to a bench where you sit and watch the sunrise. It takes you 28.0 s to walk from your house to the wind- mill and then 36.0 s to walk from the windmill to the bench. For the entire trip from your front door to the bench, what are (a) your average velocity and (b) your average speed?

6. A person jogs eight complete laps around a 400-m track in a total time of 14.5 min. Calculate ( a ) the average speed and ( b ) the average velocity, in m/s.

7. An automobile traveling 95 km/h overtakes a 1.30-km- long train traveling in the same direction on a track parallel to the road. If the train’s speed is 75 km h, how long does it take the car to pass it, and how far will the car have traveled in this time? (See the figure) What are the results if the car and train are traveling in opposite directions?

8. The position of the front bumper of a test car under microprocessor control is given by x ( t) = 2.17 m + (4.80 m/s

2

) t

2

– (0.100 m/s

6

) t

6

. (a) Find its position and acceleration at the instants when the car has zero velocity.

(b) Draw x t , v x

t , and a x

t graphs for the motion of the bumper between t = 0 and t = 2.00 s.

9. Mars Landing. In January 2004, NASA landed exploration vehicles on Mars. Part of the descent consisted of the following stages:

Stage A: Friction with the atmosphere reduced the speed from 19,300 km/h to 1600 km/h in 4.0 min.

Stage B: A parachute then opened to slow it down to 321 km/h in 94 s.

FEU ALABANG

Senior High School Program

Problem Set 1 in General Physics

Topic(s)

Measurement and Motion in Straight Line

Number of Items

15

Total Points

100

Submission Date

After 8 days

Stage C: Retro rockets then fired to reduce its speed to zero over a distance of 75 m.

Assume that each stage followed immediately after the preceding one and that the acceleration during each stage was constant. (a) Find the rocket’s acceleration (in m/s

2

) during each stage. (b) What total distance (in km) did the rocket travel during stages A, B, and C?

10. A meter stick is held vertically above your hand, with the lower end between your thumb and first finger.

On seeing the meter stick released, you grab it with these two fingers. You can calculate your reaction time from the distance the meter stick falls, read directly from the point where your fingers grabbed it. (a) Derive a relationship for your reaction time in terms of this measured distance, d . (b) If the measured distance is

17.6 cm, what is the reaction time?

11. Little Ethan plays with his remote control car, and generates the motion graph below. The car starts by moving eastwards. a. Identify section(s) where the car moves with constant velocity. b. Identify section(s) where the car moves west. c. Identify section(s) where the car speeds up. d. When is the car at rest? e. What is the average velocity of the car between 0 and 15 seconds? f. What is the average speed of the car in the same time interval? h. What is the total displacement of the car from 0 to 22 seconds? i. Draw a velocity vs. time graph describing the motion of the car.

12. Little Johnny is hiding in his tree house that is 5.0 meters above the ground. He is waiting in ambush for his brother, Tommy. Tommy, not knowing of his brother’s location or devious plans, is napping below the tree house. a. If Johnny drops the balloon from rest, how long does it take to hit Tommy? b. How fast is the balloon going when it hits Tommy? c. If Johnny throws the balloon downwards at 5 m/s, how long does it take to hit Tommy? d. Now, how fast is the balloon going when it hits Tommy?

FEU ALABANG

Senior High School Program

Problem Set 1 in General Physics

Topic(s) Number of Items Total Points Submission Date

Measurement and Motion in Straight Line 15 100 After 8 days

13. Winnie The Pooh falls out of a honey tree as shown in the figure while retrieving a hunny pot on a blustery day. a. If he fall from a height of 3 meters, what is his final velocity right before he strikes the ground? b. If Christopher Robin tries to save him, how much time does Christopher Robin have to catch Pooh

(how long is Pooh falling)?

14. Lebron James slam dunks a basketball and a physics student observes that Lebron’s feet are 1.0 meter above the floor at the peak of his jump. At what upward speed must Lebron leave the floor with to achieve this?

15. A person jumps out a fourth-story window 18.0 m above a firefighter’s safety net. The survivor stretches the net 1.0 m before comingto rest, as given in the figure.

( a ) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?

( b ) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.

Bonus – Challenge Problems (10 points)

In a lecture demonstration, a 3.0-m-long vertical string with ten bolts tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string falls on a tin plate, and the class hears the clink of each bolt as it hits the plate.

( a ) The sounds will not occur at equal time intervals. Why?

( b ) Will the time between clinks increase or decrease as the string falls?

( c ) How could the bolts be tied so that the clinks occur at equal intervals? (Assume the string is vertical with the bottom bolt touching the tin plate when the string is released.)

FEU ALABANG

Senior High School Program

Problem Set 1 in General Physics

Topic(s)

Measurement and Motion in Straight Line

Number of Items

15

Total Points

100

Submission Date

After 8 days