Assignment 10 Begin Date: 11/3/2017 8:00:00 PM -- Due Date: 11/10/2017 11:59:00
ID: 1775788 • Letter: A
Question
Assignment 10 Begin Date: 11/3/2017 8:00:00 PM -- Due Date: 11/10/2017 11:59:00 PM End Date: 11/12/2017 11:59:00 PM (7%) Problem 9: A car engine produces a constant power of P = 221 hp. The car and motor have a combined mass of m = 2470 kg Randomized Variables P = 221 hp m = 2470 kg 50% Part (a) After t-5 s what is the cars speed in m/s? You may assume no energy is required to spin the tires Grade Summary Deductions Potential 0% 100% cosO asin() tan() | | ( acos) Submissions Attempts remaining: 10 (4% per attempt) detailed view cotan) a atanacotan cosh )sinhO tanhO cotanhO END Degrees Radians DELCLEAR Submit Hint I give up! Hints: 3% deduction per hint. Hints remaining: Feedback: 4% deduction per feedback. 50% Part (b) A top fuel dragster of mass m 1000 kg can accelerate and cover 400 m in 7 secs from a dead stop. How much horsepower is the engine producing at the wheels, assuming the acceleration is constant?Explanation / Answer
power P = work/time
from work energy relation work = change in KE
W = (1/2)*m*(vf^2 - vi^2)
vi = initial speed = 0
vf = speed after t time
P = (1/2)*m*vf^2/t
1 hp = 746 watts
221*746 = (1/2)*2470*vf^2/5
speed vf = 25.8 m/s
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part (b)
fro constant acceleration
displacement = average velocity*time
400 = (vf + 0 )/2*7
vf = 114.3 m/s
work done = change in KE = (1/2)*m*(vf^2 - vi^2)
power = work/time
POWER = (1/2)*1000*114.3^2/7 = 933177.85 W
1 w = 1/746 hp
power = 933177.85/746 = 1251 hp <<<<-------ANSWER