Medgar Evers College Department of Physical, Environmental and Computer Course:
ID: 1871689 • Letter: M
Question
Medgar Evers College Department of Physical, Environmental and Computer Course: University Physics I Physies 211-001 Exam #1-2/13/201 8 Prof. W. A. Smith Answer all questions below In the area provided, show all work in order to obtain full or partial credit. Be neat. No Scrap Papers. Cell-phones, Laptops or tablets are not to be used as calculators. 1. How far does the runner whose velocity time graph is shown below travel in 20s? "( 6 5 1o 5 20 t 2. A bus driver starts from rest at a station and accelerates at a rate of 3m/s for 8 seconds. She then drives at the constant speed, the speed at the end of the 8 seconds, for 30s, and decelerates at 4m/s until she arrives and stops at the next station. Find the total distance covered by the driver.Explanation / Answer
1)
The area under the v-t graph gives the distance
for 0 to 5 s the distance is
s1 = area of triangle (1/2 * base * height)
s1 = 1/2 * 5 * 6
s1 = 15 m
for 5 to 10 s
S2 = Area of rectangle (length * breadth)
s2 = (10-5)* 6
s2 = 30 m
for 10 to 15 s
s3 = Area of triangle + Area of rectangle
s3 = (1/2 * (15-10) * (6-3)) + ((15-10)*3)
s3 = 22.5 m
for 15 to 20 s
s4 = area of rectangle
s4 = (20-15) * 3
s4 = 15 m
the total distance s = s1 + s2 + s3 + s4
s = 15 + 30 + 22.5 + 15
s = 82.5 m
2)
initial velocity u = 0 m/s
acceleration a = 3 m/s^2
t = 8 s
distance travelled s1 = (u*t) + (1/2 * a * t^2)
s1 = 0 + (1/2 *3 * 8^2)
s1 = 96 m
the velocity after 8 s is
v = u + (a*t)
v = 0 + (3 * 8)
v = 24 m/s
the distance travelled for next 30 s is
s2 = v * t
s2 = 24 * 30
s2 = 720 m
In next step
here initial velocity u = 24 m/s
final velocity v = 0
a = - 4 m/s^2
from v^2 - u^2 = 2 * a * s
0 - (24)^2 = 2 * (-4) * s3
s3 = 72 m
total distance s = s1 + s2 + s3
s = 96 + 720 + 72
s = 888 m