# Homework Help: Midterm Study Guide help

1. Jan 6, 2008

1.) A stone is thrown with an initial velocity of 7.0m/s. the acceleration of the stone is constant and has the value of -9.8m/s to the power of ((2)). What is the velocity of the stone after .50 s?

I put 2.1 not sure if it's right.

2.) An airplane starts from rest and accelerates at 10.8 m/s to power of ((2)). What is its speed at the end of a 400m long runway.

I don't really know where to begin.

3.) A displacement vector is 34.0m in length and is directed 60.0 degrees east of north. What are the components of this vector?

Again I don't even know where to begin.

It would be nice if someone could explain these to me. Thanks in advance.

2. Jan 6, 2008

### Kurdt

Staff Emeritus
For question 1.) you are correct but remember your units.

For 2 you will need another of the kinematic equations which can be found here.

https://www.physicsforums.com/showpost.php?p=905663&postcount=2

Remember what information you're given and what you need, that will help you choose.

For 3.), think of the vecto as the hypotenuse of a right angled triangle the components are the lengths of the other two sides in the north and east directions. How would you find the lengths of two sides of a right angled triangle given the hypotenuse and an angle?

3. Jan 6, 2008

Oh ok so for number 3 i would have to use sin 60 = dy/34 and cos 60 = dx/34.

And for 2 I'm not sure what equation to use is the velocity and displacement the right one?

$$v^2 = v_0^2 + 2 a \Delta x$$

4. Jan 6, 2008

### Kurdt

Staff Emeritus
Your cos and sin will be the other way round because the angle is measured from the y-axis (north).

Yes you could use the equation you've stated for 2.