# High School Physics Help

1. Sep 28, 2009

### lauralovesyou

Hi,

I have a few questions that I'm stuck on, any help would be greatly appreciated, and please show the work, so I understand how to do it.

1.If an object is dropped from a height of 2.0m, how long does it take to hit the ground?

2. A driver in a car travelling at 55km/h sees a ball roll out in the street 20m in front of the car. She slams on her brakes and decelerates at 5.0m/s^2. How long (in seconds) does it take for her to stop? How far does the car travel in this time? Does she stop in time to avoid hitting the ball?

3. A ball is thrown straight up with a speed of 20.m/s. How long does it take for the ball to reach its maximum height. What is the maximum height that the ball reaches? How fast is the ball travelling (ignoring air resistance) when it comes back to its starting point?

4. A car changes its velocity from 20 m/s (W) to 15m/s (E) in 7.0s. What is the average acceleration of the car? What is the displacement of the car over the 7.0s?

2. Sep 28, 2009

### RoyalCat

What equations do you think are relevant? How would you approach the problems?

3. Sep 28, 2009

### lauralovesyou

I honestly do not know, I've missed a whole month's worth of physics, therefore I'm very behind, I'm trying to get as much help as I can and if I can get guidance on how to do a few questions, that would be helpful. All I know is that this unit is on kinematics.

4. Sep 28, 2009

### RoyalCat

Then what you need to know is the basic kinematic equations for motion under constant acceleration.

Before we start, I'll ask you this, do you know basic calculus?

Does the following expression ring any bells, or is it a bit scary:

$$\vec v = \frac{d\vec x}{dt}$$