Speed and Acceleration
Part 1: Concepts
1. Does the speedometer of a car read average speed or instantaneous speed? ______instantaneous (1point) ______
How do you know? b/c the speedometer moves back and forth. It does not show how far you’ve traveled, or how long it took you to travel that distance. (1point)
2. If the speedometer in a car shows 40 km/hr for an hour, can you say the car has a constant velocity? __no (1point) Explain your answer. It is not known if the direction of the vehicle changed during that hour. (1point)
3. What two controls on a car cause a change in speed? Accelerator and brake (1point)
What control causes a change in velocity? Steering wheel, brake, accelerator (1point)
4. What is the acceleration of a car that travels in a straight line at a constant speed?
0 (not changing speed or direction) (2 points)
5. Describe a situation in which you can accelerate even though your speed doesn’t change.
Changing your direction (1point)
Part 2: Calculations - Speed
6. It takes Serina 0.25 hour to drive to school. Her route is 16 km long. What is Serina’s average speed on her drive to school?
Given:t = .25 hr (3 points)
d = 16km
Formula:
s = d/t (2 points) / Work:
s = 16km/.25 hr (5 points)
Answer:
64 km/hr (5 points)
7. In a competition, an athlete threw a flying disk 139 meters through the air. While in flight, the disk traveled at an average speed of 13.0 m/s. How long did the disk remain in the air?
Given:d = 139m (3 points)
s= 13m/s
Formula:
t = d/s (2 points) / Work:
t = 139m/13 m/s (5 points)
Answer:
10.69 s (5 points)
8. Josh rolled a bowling ball down a bowling alley at an average speed of 7.2 m/s. It took 2.5 s for the ball to reach the pins. How long was the bowling alley?
Given:t = 2.5 s (3 points)
s= 7.2 m/s
Formula:
d = s*t (2 points) / Work:
d = 7.2 m/s * 2.5 s (5 points)
Answer:
18 m (5 points)
Part 3: Calculations - Acceleration
9. Usain Bolt accelerates from 0 m/s to 10.44 m/s in 9.58s. What is his acceleration?
given:tf = 9.58 s
ti = 0s (3 points)
vi = 0 m/s
vf= 10.44 m/s
formula:
acc = vf – vi (2 points)
tf – ti / work:
a= 10.44m/s - 0m/s (5 points)
9.58s - 0s
answer:
a= 1.09 m/s/s (5 points)
or
= 1.09 m/s2
10. A runner covers the last straight stretch of a race in 4 s. During that time, he speeds up from 5 m/s to 9 m/s. What is the runner’s acceleration in this part of the race?
given:tf = 4s
ti = 0s (3 points)
vi = 5m/s
vf= 9m/s
formula:
acc = vf – vi (2 points)
tf – ti / work:
a= 9m/s-5m/s (5 points)
4s - 0s
answer:
a= 1m/s/s (5 points)
11. A train going 55 mi/hr takes 144 s to come to a complete stop. What is the trains acceleration?
given:tf = 144 s
ti = 0 s (3 points)
vi = 55 mi/hr
vf= 0 mi/hr
formula:
acc = vf – vi (2 points)
tf – ti / work:
a= 0 mi/hr – 55 mi/hr
144s - 0s
answer:
a= -0.38 mi/hr/s or a = -0.38 mi/hr/s (5 points)