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# don't understand the markscheme? watch

1. Hello! I was doing a WJEC Additional Science P2 Paper and this answer is tripping me up...
The question states

'One of the world's tallest roller coasters has an initial peak of height 140m. After reaching the top, the car first falls to a height 50m above the ground before it continues on its journey
-the mass of the car and passengers is 1200kg, use equations from page 2 to calculate the theoretical maximum velocity of the car after this first fall (g=10m/s²)"

Now, I did
PE = mgh
= 1200 x 10 x (140-50) = 1080000J

then PE=KE, so KE = 1/2mv²
1080000 = 1/2 x 1200 x v²
I rearranged and got 21.21 etc
But the mark scheme says the velocity is double, 42.4 m/s

2. (Original post by CresentHan)
Hello! I was doing a WJEC Additional Science P2 Paper and this answer is tripping me up...
The question states

'One of the world's tallest roller coasters has an initial peak of height 140m. After reaching the top, the car first falls to a height 50m above the ground before it continues on its journey
-the mass of the car and passengers is 1200kg, use equations from page 2 to calculate the theoretical maximum velocity of the car after this first fall (g=10m/s²)"

Now, I did
PE = mgh
= 1200 x 10 x (140-50) = 1080000J

then PE=KE, so KE = 1/2mv²
1080000 = 1/2 x 1200 x v²
I rearranged and got 21.21 etc
But the mark scheme says the velocity is double, 42.4 m/s

Yeah I got 42.43 as well - probably you're not rearranging properly

1080000 = 1/2 x 1200 x v2
2160000 = 1200 x v2
1800 = v2
v = sqrt (1800) = 42.43

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