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How do I do these two fairly basic Mechanics questions?

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For part 1) I know that acceleration is the change in speed/time taken, but I dont have the time taken. How can I do this one?

And How do I do part 2?

Thanks!
do you know the suvat equations
You need to learn your SUVAT equations :smile: They are;
V=U+AT
S=UT+(0.5A*T^2)
S=0.5(U+V)T
V^2 = U^2 + 2AS
S=VT-(0.5A*T^2)

Where U = initial velocity, V = Final velocity, A = acceleration, T = time and S = displacement. Also, ^2 means squared; is hard to write on a comp XD

So for question one, you know the U is 0, V is 20 m/s, and S is 100m. Were trying to find A. So youd use the 4th equation. Subbing in we get;

(20)^2 = (0)^2 + 2(A)(100)

Expanding out;

400 = 200A

So the acceleration = 2m/s^2

For question 2;

Convert all units into Km/h instead of M/h; so 24mph = 38.4km/h = 38400m/h = 10 2/3 m/s

So you know her U = 10 2/3 m/s, her A = -0.2m/s^2 (- because its a deceleration), the T = 60s and were trying to find S. So wed use equation 2.

Subbing in;

S = (10 2/3)(60) +(0.5(-0.2)(60^2))

Expanding out;

S = 640 + (-360)

S = 280m
this is what i got, but its based on the assumption that the skier reaches 20ms-1 at the base of the cliff


C)16ms^-2

s=100
u=0
v=20
a=?
t=don't need

rearrange v^2=u^2+2as to get a on its own.
(v^2-u^2)/2s=a
which is (20^2)/25 =16

d)1km

24mph= 32/3 ms^-1

s=?
u=32/3
v= don't need
a=o.2
t=
60
use s=ut+0.5at^2

let s=(32/3)x60 +(0.5x0.2x60^2)= 1000m

which gives you 1000m which is 1 km

probably double check this, I haven't done mechanics since the summer
Original post by Mr.McNuggets
this is what i got, but its based on the assumption that the skier reaches 20ms-1 at the base of the cliff


C)16ms^-2

s=100
u=0
v=20
a=?
t=don't need

rearrange v^2=u^2+2as to get a on its own.
(v^2-u^2)/2s=a
which is (20^2)/25 =16

d)1km

24mph= 32/3 ms^-1

s=?
u=32/3
v= don't need
a=o.2
t=
60
use s=ut+0.5at^2

let s=(32/3)x60 +(0.5x0.2x60^2)= 1000m

which gives you 1000m which is 1 km

probably double check this, I haven't done mechanics since the summer


Your method looks right but a lot of your calculations look a bit off; in the first one 2s is 200 not 25...and in the second one I think your conversion from mph to km/h is off
Original post by greenfeather
Your method looks right but a lot of your calculations look a bit off; in the first one 2s is 200 not 25...and in the second one I think your conversion from mph to km/h is off


damn my bad, i don't know how i read the numbers in the first one wrong. but i think the second part is right.
if the conversion is off then... well ****

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