Mechanics question

Watch
Announcements
Thread starter 1 year ago
#1
Question:
Eddy cycles up a hill. His mass, together with his bicycle, is 92 kg. His driving force is 125 N and resistance from friction is 45 N. Eddy travels 350 metres along the road which rises through a vertical height of 32 metres. His starting speed is 8.2 m s−1. Find his final speed.

I know the formulae but I cant get the right answer.
0
Thread starter 1 year ago
#2
help
0
1 year ago
#3
(Original post by Rico07)
Question:
Eddy cycles up a hill. His mass, together with his bicycle, is 92 kg. His driving force is 125 N and resistance from friction is 45 N. Eddy travels 350 metres along the road which rises through a vertical height of 32 metres. His starting speed is 8.2 m s−1. Find his final speed.

I know the formulae but I cant get the right answer.
What have you tried?

Find the gain in KE by considering energy and work done
Hence find final speed
0
1 year ago
#4
what’s the answer (don’t wanna give u the wrong method)?
0
1 year ago
#5
You’ll need to use a mix of SUVAT and F=MA. What is the answer, I’ll do it in a sec and see if I can get the correct answer for you.
0
Thread starter 1 year ago
#6
(Original post by BobbJo)
What have you tried?

Find the gain in KE by considering energy and work done
Hence find final speed
Thats where im struggling. Is it rght to say Final Kinetic + Final GPE = Initial Kinetic - Energy lost ?
0
1 year ago
#7
(Original post by Rico07)
Thats where im struggling. Is it rght to say Final Kinetic + Final GPE = Initial Kinetic - Energy lost ?
No
Final KE = Initial KE + Work done by driving force - Work done against friction - gain in GPE
0
Thread starter 1 year ago
#8
(Original post by BobbJo)
No
Final KE = Initial KE + Work done by driving force - Work done against friction - gain in GPE
Ah that makes sense. Thank you thats all I needed.
0
1 year ago
#9
(Original post by Rico07)
Question:
Eddy cycles up a hill. His mass, together with his bicycle, is 92 kg. His driving force is 125 N and resistance from friction is 45 N. Eddy travels 350 metres along the road which rises through a vertical height of 32 metres. His starting speed is 8.2 m s−1. Find his final speed.

I know the formulae but I cant get the right answer.
(Original post by Rico07)
Ah that makes sense. Thank you thats all I needed.
The content of energy concept in A level is usually easy but it is a well-known fact that many teachers are not teaching it properly for students to approach energy or work problems systematically.

I understand that you had already worked out the answer to the question. But I suggest that you try to approach such question in a systematic way in future.

The general approach is:
1. Choose a system based on the problem
2. Write down the conservation of energy equation for the system (avoid writing initial total energy is equal to final total energy as this tends to cause some confusion. Students who write such equation usually don’t know what is the system that they have chosen.)

(Original post by Rico07)
Thats where im struggling. Is it rght to say Final Kinetic + Final GPE = Initial Kinetic - Energy lost ?
(Original post by BobbJo)
No
Final KE = Initial KE + Work done by driving force - Work done against friction - gain in GPE

A better form of conservation of energy equation
ΔKE of system + ΔPE of the system = Work done on the system by external agents
0
X

new posts
Back
to top
Latest
My Feed

Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

See more of what you like onThe Student Room

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

Poll

Join the discussion

Are you travelling in the Uni student travel window (3-9 Dec) to go home for Christmas?

Yes (50)
30.12%
No - I have already returned home (23)
13.86%
No - I plan on travelling outside these dates (37)
22.29%
No - I'm staying at my term time address over Christmas (15)
9.04%
No - I live at home during term anyway (41)
24.7%