M2 Edexcel Help

jakegreen

Can Anyone Please Give Me A Hand On Exercise 3c Of Mechanics 2, Edexcel. It Is Question 16, 17, 18. Thanks A Lot!!!

Reply 1

Nylex

10

Post the questions, I don't have a copy of the book.

Reply 2

jakegreen

OP

A cyclist starts from rest and freewheels down a hill inclined at arcsin 1/20 to horizontal. After travelling 80m the road becomes horizontal and cyclist travels another 80m before come to rest without brake use. Given that the combined mass of cyclist and machine is 80kg, model cyclist as particle and hence, find resistive force, assumed constant throughout.

A boy and his skateboard have mass of 50kg. He descends a slope inclined at 12 degrees to horizontal starting from rest. At bottom, ther ground becomes hroizontal for 10m and rise again 8 degress to horizontal. The boy travels 30m up the incline before coming to rest again. He is subject to constant resistance of 20N throughout motion. By modelling the boy and his skateboard as a single particle find distance travelled by boy down slope.

thanks

Reply 3

john !!

14

jakegreen

A cyclist starts from rest and freewheels down a hill inclined at arcsin 1/20 to horizontal. After travelling 80m the road becomes horizontal and cyclist travels another 80m before come to rest without brake use. Given that the combined mass of cyclist and machine is 80kg, model cyclist as particle and hence, find resistive force, assumed constant throughout.

I'm only halfway through M1 but I'll have a go.

Use trigonometry to find the vertical distance he travelled, and then take g and their combined masses to calculate the potential energy he lost from the decline.

Then use that figure to work out his velocity at the point of the road becoming horizontal, since change in g.p.e. is equal to k.e, you can equate your first answer to 1/2mv^2. Then use newton's equations, given the distance, the initial velocity your answer when you solve the g.p.e=k.e. equation, and the final velocity which is taken to be 0, to find the negative acceleration of the bike.

Given the mass of them combined you can then find the force acting against the bike which is caused purely by friction (remember, without friction he would continue to cycle forever).

Reply 4

john !!

14

jakegreen

A boy and his skateboard have mass of 50kg. He descends a slope inclined at 12 degrees to horizontal starting from rest. At bottom, ther ground becomes hroizontal for 10m and rise again 8 degress to horizontal. The boy travels 30m up the incline before coming to rest again. He is subject to constant resistance of 20N throughout motion. By modelling the boy and his skateboard as a single particle find distance travelled by boy down slope.

This one is very similar. Try it yourself using the equations

potential energy lost = kinetic energy gained

or

mgh (mass * gravity * height) = 1/2mv^2 (half of the mass time the velocity squared)

and newton's equations of motion.

I don't want to answer them all cos then you don't learn anything. :tongue:

Also I have my own chemistry to do. :frown:

Reply 5

elpaw

15

jakegreen

A cyclist starts from rest and freewheels down a hill inclined at arcsin 1/20 to horizontal. After travelling 80m the road becomes horizontal and cyclist travels another 80m before come to rest without brake use. Given that the combined mass of cyclist and machine is 80kg, model cyclist as particle and hence, find resistive force, assumed constant throughout.

cyclyst is particle bla bla bla

GPE lost = 1/20 * 80 * 80 = 320J

WD = FD = F(160) = 320J

=> F = 2N

jakegreen

A boy and his skateboard have mass of 50kg. He descends a slope inclined at 12 degrees to horizontal starting from rest. At bottom, ther ground becomes hroizontal for 10m and rise again 8 degress to horizontal. The boy travels 30m up the incline before coming to rest again. He is subject to constant resistance of 20N throughout motion. By modelling the boy and his skateboard as a single particle find distance travelled by boy down slope.

GPE lost = sin(12) * L * 50 + sin(8) * 30 * 50

WD = (L + 30) * 20

GPE lost = WD => L = (do it yourself)

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