M2 power rep available Watch

This discussion is closed.
realicetic
Badges: 1
Rep:
?
#1
Report Thread starter 13 years ago
#1
this guy cycles up a slope (combined mass of bike and guy is 80kg) inclined at arcsinx=1/7 to the horizontal. Resistance against motion = 40N and he travels at a constant speed of 6m/s.

a) find the power exerted by the man
b)If the man suddenly increases his workrate by 240 W, find the magnitude of his acceleration up the slope at this instant.

I have done a) and got 912W but dont know how to do b)
the answer to b) is 0.5 m/s^-2

please help!!!
0
Christophicus
Badges: 18
Rep:
?
#2
Report 13 years ago
#2
this guy cycles up a slope (combined mass of bike and guy is 80kg) inclined at arcsinx=1/7 to the horizontal. Resistance against motion = 40N and he travels at a constant speed of 6m/s.

a) find the power exerted by the man
Equation of motion parallel to slope
F - 40 - 80gsinx = ma
F - 40 - 80gsinx = 0
F = 40 + 80gsinx
F = 40 + 80[9.8][1/7]
F = 152N

Power = Force x velocity
Power = 152 x 6

Power = 912W

b)If the man suddenly increases his workrate by 240 W, find the magnitude of his acceleration up the slope at this instant.

I have done a) and got 912W but dont know how to do b)
the answer to b) is 0.5 m/s^-2

please help!!!
Equation of motion parallel to slope
F - 40 - 80gsinx = ma
F - 40 - 80[9.8][1/7] = 80a
F - 40 - 112 = 80a

Power = Force x velocity
1152 = Fv
1152 = 6F
F = 1152/6 = 192N

a = [F - 40 - 112]/80
a = [192 - 40 - 112]/80
a = 40/80
a = 0.5ms-2
0
realicetic
Badges: 1
Rep:
?
#3
Report Thread starter 13 years ago
#3
Equation of motion parallel to slope
F - 40 - 80gsinx = ma
F - 40 - 80[9.8][1/7] = 80a
F - 40 - 112 = 80a

Power = Force x velocity
1152 = Fv
1152 = 6F
F = 1152/6 = 192N

a = [F - 40 - 112]/80
a = [192 - 40 - 112]/80
a = 40/80
a = 0.5ms-2[/QUOTE]

ok thanx. the thing that confuses me is why velocity remains 6ms-1 when acceleration has increased
0
Narin
Badges: 0
Rep:
?
#4
Report 13 years ago
#4
The key is the phrase "at this instant."
He has just, at that moment, increased his power, so meaning that his acceleration will be greater, but there hasn't been time for his velocity to actually have increased yet, if you get what I mean.
0
realicetic
Badges: 1
Rep:
?
#5
Report Thread starter 13 years ago
#5
(Original post by Narin)
The key is the phrase "at this instant."
He has just, at that moment, increased his power, so meaning that his acceleration will be greater, but there hasn't been time for his velocity to actually have increased yet, if you get what I mean.
yeah thanx alot i know what u mean. well explained lol
0
X
new posts
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

University open days

  • Cranfield University
    Cranfield Forensic MSc Programme Open Day Postgraduate
    Thu, 25 Apr '19
  • University of the Arts London
    Open day: MA Footwear and MA Fashion Artefact Postgraduate
    Thu, 25 Apr '19
  • Cardiff Metropolitan University
    Undergraduate Open Day - Llandaff Campus Undergraduate
    Sat, 27 Apr '19

Have you registered to vote?

Yes! (125)
39.56%
No - but I will (17)
5.38%
No - I don't want to (20)
6.33%
No - I can't vote (<18, not in UK, etc) (154)
48.73%

Watched Threads

View All