1. PHYS 2010 Nathalie Hoffmann University of Utah
Wednesday 5/20
PHYS 2010
Nathalie Hoffmann
University of Utah

2. Distance vs. Displacement
What differences are there?

3. Distance vs. Displacement
What differences are there?
Distance: scalar
Displacement: vector
Distance: always positive
Displacement: has direction (1D: plus/minus, 2D: angle w.r.t. x/y axis, etc.)

4. Speed vs. Velocity
Differences?

5. Speed vs. Velocity Differences? Speed: scalar (always positive)
Velocity: vector (i.e. has direction)
Speed = distance/time (interval)
Velocity = displacement/time (interval)
NOTE: average speed does not necessarily equal magnitude of velocity

6. Acceleration What does it mean for an object to be accelerated?
Examples
Acceleration does not necessitate speeding up

7. Kinematics Equations (constant acceleration)

8. More Vector Problems
The drawing shows a force vector that has a magnitude of 475 Newtons. Find the (a) x, (b) y, and (c) z components of the vector.
What are the x and y components of the vector that must be added to the following three vectors, so that the sum of the four vectors is zero? Due east is the +x direction, and due north is the +y direction.

9. Kinematics Problems
For each of the three pairs of positions listed in the following table, determine the magnitude and direction (positive or negative) of the displacement.
Now, suppose the data in the above table describe the initial and final positions of a moving car. The elapsed time for each of the three pairs of positions listed in the table is 0.50 s. Determine the average velocity (magnitude and direction) for each of the three pairs. Note that the algebraic sign of your answers will convey the direction.

10. More Problems
 The Olympic record for the marathon set in 2008 is 2 h, 6 min,32 s. The marathon distance is 26.2 mi. What was the average speed of the record-setting runner in km/h? (1 mile = km)
A car traveling 80.0 km/h is 1500 m behind a truck traveling at km/h. How long will it take the car to catch up with the truck?
Alcohol consumption slows people’s reaction times. In a controlled government test, it takes a certain driver s to hit the brakes in a crisis when unimpaired and 1.00 s when drunk. When the car is initially traveling at 90.0 km/h, how much farther does the car travel before coming to a stop when the person is drunk compared to sober?

11. More Problems
 A runner starts from rest and achieves a maximum speed of m/s. If her acceleration is 9.77 m /s2, how long does it take her to reach that speed?
In reaching her destination, a backpacker walks with an average velocity of 1.34 m/s, due west. This average velocity results because she hikes for 6.44 km with an average velocity of 2.68 m/s, due west, turns around, and hikes with an average velocity of m/s, due east. How far east did she walk?

12. More Problems
 A car is traveling at 20.0 m/s, and the driver sees a traffic light turn red. After s (the reaction time), the driver applies the brakes, and the car decelerates at 7.00 m/s2. What is the stopping distance of the car, as measured from the point where the driver first sees the red light?
A jogger accelerates from rest to 3.0 m/s in 2.0 s. A car accelerates from 38.0 m/s to 41.0 m/s also in 2.0 s.
(a) Find the acceleration (magnitude only) of the jogger.
(b) Determine the acceleration (magnitude only) of the car.
(c) Does the car travel farther than the jogger during the 2.0 s? If so, how much farther?