# Homework Help: Physics Kinematics correction

1. May 31, 2014

### Physicsrapper

Hi, I have some questions regarding Kinematics:

1. If an object is accelerating at 9.8 m/s^2, how much time does it Need to reach ten percent of the Speed of light?

Speed of light: 299 792 458 m / s -> 10% -> 299 792 45,8 m / s

t = v/a -> 299 792 45,8 m / s / 9.8 m/s^2 = 3 059 106.714 s = 849.8 h

2. An object is uniformly accelerated at a = 4m/s^2. At time t, the object has a velocity v = 50 m/s. What is its velocity before and afterwards?

t = v/a = 50m/s / 4m/s^2 = 12.5 s

7.5s * 4m/s^2 = 30 m/s
17.5 s * 4m/s^2 = 70 m/s

3. The fastest dragster reaches 632 km/h in 3.72s. Find its average acceleration.

a=v/t -> 175.6m/s / 3.72s = 47.2m/s^2

Are all my Solutions true?

2. May 31, 2014

Correct
This question does not make much sense to me. What do you mean by before? How many seconds before? Howmany seconds afterwards?
Correct

3. May 31, 2014

### Physicsrapper

This question does not make much sense to me. What do you mean by before? How many seconds before? Howmany seconds afterwards?

Sorry, it's 5s.
Thank you for the correction!