6.

a) Read the question well. It asks you for the final speed after breaking, not after accelerating from rest.

Can you try it again?

b) Uh...

But that's still not the answer. You didn't include the distance covered while braking.

If you draw a quick sketch of the vt graph of the motion of the car, you get the area of a triangle and a trapezium to find. Try this part again too.

7.

a) You didn't square the speed... wrong answer.

b) Where did you get that formula? The actual formula is

What you are using doesn't exist and might be close to but that's not it. Try again.

c) Uh... if it took t seconds to reach the highest point (obtained in part b), then it will take t seconds to fall down from the highest point... You don't need to calculate again.

Spoiler:

Or you can use where s = 0, t becomes easy to find. Oh, I find that you need to use this equation after reading the next part.

d) Now that you know the time, find the final speed using:

8. For this one, if you don't know the cosine rule, you'll need to use Pythagoras' Theorem together with some trigonometric ratios.

Make a sketch. (This is very helpful in all sorts of problems)

When done, you'll find something like this:

You'll need to find x and y first, then use those values to find z, represented by the red broken line.

Then, you'll need to find the angle the red broken line makes with the horizontal line to get the direction C is from A.