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# Can anyone help me with physics?

I've manage to solve all of the problems except these. If anyone can help and show me how you solved these problems it would be of great help! Yes this is homework and no I'm just here to get people to do my homework. I really need help and no one is available to help me at the moment. Even if you don't give me the answer at least please start me off or guide me in the right direction.

1 - An electric vehicle starts from rest and accelerates at a rate of 2.0 m/s^2 in a straight line until it reaches a speed of 20 m/s. The vehicle then slows at a constant rate of 1.0 m/s^2 until it stops

- How much time elapses from start to stop?

- How far does the vehicle travel from start to stop?

2 - The brakes on your automobile are capable of slowing down your car at a rate of 5.0 m/s^2. - If you are going 144 km/h and suddenly see a state trooper, what is the minimum time in which you can get your car under the 90 km/h speed limit?

3 - A hot-air balloon is ascending at the rate of 12 m/s and is 69 m above the ground when a package is dropped over the side.

- How long does the package take to reach the ground?

- With what speed does it hit the ground?

4 - A hot rod can accelerate from 0 to 65 km/h in 5.3 s.

- What is its average acceleration, in m/s^2, during this time?

- How far will it travel during the 5.3 s, assuming its acceleration is constant?

- How much time would it require to go a distance of 0.33 km if its acceleration could be maintained at the value in (a)?

Any help would be greatly appreciated!

Thank you!

### 2 Answers

- 10 years agoFavorite Answer
1) If you're accelerating at 2 m/s^2, it takes ten seconds to reach 20 m/s. 20/2=10. Fairly straightforward. By the same token, it takes 20 seconds to get back to 0, so the total time is 30 seconds. To get the distance, you need the integral of the velocity. That would be one right triangle with legs of 20 and 10 and one right triangle with legs of 20 and 20. Do the math for that and you'll have the total distance.

2) To get from 144 to 90 at a rate of losing 5 per second will take 10.8 seconds. Simple subtraction and division.

3) This one's a little harder. A dropped object falls at a rate of 9.8m/s^2, but the balloon is rising. The equation looks like this:

x = (1/2) a*t^2 + v0*t + x0

where x is the final position (in this case 0), a is the rate of acceleration (-9.8m/s^2 because it's falling down), t is the time you're looking for, v0 is the original velocity (12 m/s), and x0 is the original position (69 m). You can plug that in yourself.

The equation for final velocity (v) is v = a*t + v0, so you can figure that out yourself too.

I'm assuming you can work your way through the final one from there.

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- biesLv 43 years ago
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