Normanhurst Boys Questions (1 Viewer)

[scaryshark09]

 

[scaryshark09]

for 9, i knew it was C or D
when i differentiated the velocity function, it was positive, so doesnt that mean speed is increased
i also tested similar time points and the velocity seemed to be increasing.
but the answer is D somehow

for 4, i have no idea

 

[user18181818]

for 9 if u differentiate it you get 6costsint and then sub 5pi/6 in that it's negative - therefore D
what's the answer to 4?

 

[scaryshark09]

for 9 if u differentiate it you get 6cost and then sub 5pi/6 in that it's negative - therefore D
what's the answer to 4?

the derivative is 6costsint and yes i know that its negative when you sub in, but that doesn't mean that the speed is decreasing, that just means that the speed is in the negative direction

 

[scaryshark09]

i understand 4 now (C), but can someone explain why the speed is decreasing in question 9?

 

[AsuTeksu]

Like @user18181818 said, the derivative is 6cosxsinx and if you substitute t=5π/6, you get -2.5980.... which is decreasing speed since the gradient is negative, thus, D.

 

[user18181818]

how do u do 4

 

[scaryshark09]

Like @user18181818 said, the derivative is 6cosxsinx and if you substitute t=5π/6, you get -2.5980.... which is decreasing speed since the gradient is negative, thus, D.

i disagree.
that doesnt mean that the speed is decreasing

 

[scaryshark09]

how do u do 4

just draw graphically and then there are 2 points of intersection

 

[scaryshark09]

Like @user18181818 said, the derivative is 6cosxsinx and if you substitute t=5π/6, you get -2.5980.... which is decreasing speed since the gradient is negative, thus, D.

that just means the speed is in the negative direction, but that doesnt matter for thisn question as speed is a scalar quantity. you have to differentiate again to find the gradiant of the speed to find out if its increasing or decreasing. and this is positive. so shouldnt the answer be C?

 

[scaryshark09]

@carrotsss @synthesisFR

 

[carrotsss]

hi

 

[scaryshark09]

hi

can you explain 9

 

[DVNG]

that just means the speed is in the negative direction, but that doesnt matter for thisn question as speed is a scalar quantity. you have to differentiate again to find the gradiant of the speed to find out if its increasing or decreasing. and this is positive. so shouldnt the answer be C?

As you said you have to differentiate again. This gives you the acceleration which is positive, also as you said. A positive acceleration means the particle is being pushed to the right, while a negative velocity means the particle is moving to the left. Since it is moving to the left but being pushed to the right, it is slowing down

 

[scaryshark09]

how come they divide by 2 in part (i) but not (ii)??

 

[synthesisFR]

View attachment 40787View attachment 40788
how come they divide by 2 in part (i) but not (ii)??

how many papers r u doing and which questions and wher eu getting the q fromm

 

[scaryshark09]

wher eu getting the q fromm

read the title of this thread

 

[scaryshark09]

can someone explain when and when not to divide by 2?
and why do you even need to divide by 2?
if theres 12 people in a line, and you choose 6, how is this double the answer? @carrotsss

 

[carrotsss]

can someone explain when and when not to divide by 2?
and why do you even need to divide by 2?
if theres 12 people in a line, and you choose 6, how is this double the answer? @carrotsss

It’s the same deal as last time, for each possibility you also have an identical possibility with the groups swapped, so in order to cancel this out you halve it. the reason part 2 is different is because there are 2 people who have been fixed in one group and hence there is never an identical possibility where everyone’s in the other group because they’re never in the other group themselves