Question

Pls help
The cyclist is applying a forward push with pedals of 80N, while there is a backward frictional force of 60N. The mass of the cyclist and bicycle is 100kg and bicycle is initially at rest.

A. Calculate the speed of the bicycle after 12seconds
B. what time will it take the bicycle to slow down and stop
C. calculate the total distance traveled during the whole journey

Answer 1

@Owlcoffee @ganeshie8

Answer 2

@almaa @alekos

Answer 3

use newton's second law :
\[F_{net}=ma\]

Answer 4

we need to find the speed

Answer 5

Yes. and net force = applied force - frictional force

Answer 6

no it is ma

Answer 7

Once you have acceleration, you can find the speed using equations like \(v=u+at\) etc

Answer 8

the net force is 20N

Answer 9

u is 0

Answer 10

so
v = 20*12

Answer 11

right, so 20N is acting on the cyclist-bicycle system.
find the acceleration produced on the system by that net force

Answer 12

20/100 = 0.2

Answer 13

v= 0.2*12

Answer 14

looks good. that means, 20N force acting on the cylcist-bicycle system for 12 seconds, increases the speed from 0 m/s to 2.4 m/s

Answer 15

yes for b

Answer 16

quesiton b is not clear

Answer 17

ok, c

Answer 18

c makes no sense too

Answer 19

it does

Answer 20

is it given that the cyclist has stopped applying force on the pedals at 12th second ?

Answer 21

isnt b 12seconds

Answer 22

again, both parts b and c make no sense because the question doesn't give any info on when/how the breaks are applied

Answer 23

If you want to show some work to your teacher, you may assume that the force on pedals was removed at 12th second and the bicycle slows down and stops due to friction

Answer 24

it says if after 12seconds the cyclist stops padeling so what will happen to the motin

Answer 25

i did not put that bc i knew the answer

Answer 26

then it aks the b question

Answer 27

lol okay, you should put the complete question

Answer 28

sorry man

Answer 29

i think that the fiction increases

Answer 30

to my limited knowledge, friction disappears as soon as the cyclist removes the force on pedals.

friction acts only when the bicycle accelerates... so, strictly speaking, friction cannot stop the bicycle because the friction disappears after the cyclist stops pedalling.

i could be completely wrong in this matter, lets check with experts
@mathmate @UnkleRhaukus

Answer 31

thats why it stops because of the surface fiction increasing

Answer 32

the fiction increases for sure

Answer 33

i think so

Answer 34

@UnkleRhaukus

Answer 35

If you don't apply breaks on wheels, and if there is no air drag,
then i guess bicycle should never stop because the bicycle is under pure rolling(relative velocity between road and wheels is 0)

Answer 36

air drag is also a fiction

Answer 37

i think the fiction increases

Answer 38

right @UnkleRhaukus

Answer 39

are you saying 60N is the air resistance ?
that makes no sense too because air resistance must depend on the velocity of bicycle, it is never constant..

Answer 40

no its friction while you cycle

Answer 41

friction from road?