Physics I Practice Problems For Dummies (+ Free Online Practice). Dummies Consumer

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Chapter 2

      Moving along with Kinematics

      To describe motion, you can use terms like displacement, speed, velocity, and acceleration. Displacement is a distance in a particular direction. Speed is the distance traveled in a certain amount of time. If you combine speed with a direction, you get velocity. Acceleration measures how quickly velocity changes.

       The Problems You’ll Work On

      In this chapter you’ll move through the following topics:

      ✓ Finding the displacement in one and two dimensions

      ✓ Using velocity to determine the displacement

      ✓ Taking the average of the instantaneous speed

      ✓ Determining the change in velocity using acceleration

      ✓ Relating displacement, velocity, acceleration, and time

       What to Watch Out For

      You’ll speed through these questions if you keep the following in mind:

      ✓ Using the distance traveled, not the displacement, to determine average speed

      ✓ Remembering that velocity is the change in displacement in a certain amount of time

      ✓ Remembering that acceleration is the change in velocity in a certain amount of time

Determining Displacement Using Positions in One Dimension

      26–29

       26. You leave your apartment and walk 2 blocks north, only to realize that you forgot your keys. You turn around and walk back 2 blocks south to get them. What is your total displacement?

       27. A car is driven north for 5 miles, then south for 3 miles, and then north again for 2 miles. What is its displacement?

       28. A pair of figure skaters skates together for 10 meters. Then the man launches his partner through the air. She lands 15 meters ahead of where the pair began skating. What is her displacement with respect to the launching point when she lands?

       29. An elevator is at the ground floor. It goes once to the first floor, twice to the second floor, three times to the third floor, and then four times to the fourth floor. What is the displacement of the elevator when Ms. Smith gets on at the third floor?

Getting Displacement in Two Dimensions with Axes

      30–35

       30. You move a marker on a board from one point (2 centimeters, 4 centimeters) to another point (5 centimeters, 8 centimeters). What is the magnitude of the displacement of the marker?

       31. To get to your friend’s house, you walk 4 blocks north and 1 block east. What is the direction of your displacement with respect to the direction east?

       32. A basketball player shoots the ball, releasing it at 8 feet above the floor and 5 feet from the basket. The ball goes straight through the basket, which is 10 feet above the floor. What is the magnitude of the displacement of the ball from the point at which it is released and the point at which it passes through the hoop?

       33. A chess board is 8 squares by 8 squares. You move your bishop from one square (3, 1) to another square (7, 5). What is the magnitude (in squares) and angle of the displacement?

       34. A child is scooting around on his toy truck. He scoots 5 meters down the hall, then turns 90 degrees to the right and scoots 3 meters, then turns again 90 degrees to the right and scoots 2 more meters. What is his displacement over this trip?

       35. You want to shoot a laser beam from the edge of a stage to a disco ball hanging from the ceiling. The stage is 1 meter above the floor, the disco ball is 1 meter below the ceiling, and the height of the ceiling is 4 meters. The horizontal distance from the edge of the stage where the laser is mounted to the point directly under the disco ball is 5 meters. At what angle above the horizontal should you aim the laser?

Traveling with Average Speed and at Instantaneous Speed

      36–40

       36. You run from your house to the grocery store in 1.0 minute, and the store is 300 meters from your house. What is your average speed in meters per second for the trip?

       37. In a traffic jam, you drive at 10 miles per hour for 10 minutes, at 20 miles per hour for 1 minute, at 15 miles per hour for 5 minutes, at 30 miles per hour for 2 minutes, and at 5 miles per hour for 15 minutes. What is your maximum instantaneous speed?

       38. A ball is dropped from the top floor of your five-floor apartment building. You’re on the bottom floor and see the ball go past your small window. If you measure the ball’s speed at this point, is it the average speed, the instantaneous speed, both the average and the instantaneous speed, or neither the average nor the instantaneous speed?

       39. The average speed of a car being driven in London is 11 miles per hour. If you have to drive 15 miles from your home to work in London, how long do you expect it to take?

       40. The average speed of runner A is 10 percent greater than that of runner B. If runner B is given a 10-meter head start in a 100-meter dash, which runner will finish first?

Distinguishing between Average Speed and Average Velocity

      41–45

       41. You travel north for 80 miles and then east for 30 miles. What is the magnitude of your average velocity if the entire trip takes 4 hours?

       42. You travel north for 80 miles and then east for 30 miles. What is your average speed if the entire trip takes 4 hours?

       43. You travel 35 miles north and 20 miles east. If the trip takes 30 minutes, what is the magnitude (in miles per hour) and direction of your average velocity?

       44. A postman walks 10 blocks north, then 3 blocks east, and then south for an unknown number of blocks. The time for his trip is 1.0 hour, and each block is 100 meters long. If his average speed is 1.0 meter per second, what is the magnitude of his average velocity in meters per second?

       45. You travel 40 miles north, then 30 miles east, then 20 miles north, and then 10 miles south. If your trip takes 2 hours, what is your average speed?

Speeding Up and Down with Acceleration

      46–50

       46. It takes you 2.0 seconds to accelerate from a standstill to a running speed of 7.0 meters per second. What is the magnitude of your acceleration?

       47. The acceleration due to gravity at the surface of Earth is about 9.8 meters per second per second. If you drop a small heavy ball from the fourth floor of a building, how fast is the ball moving after 0.5 seconds?

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