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Kinematics
Kinematics is the study of how a body moves. This includes linear motion, angular motion, and rotational motion.
3,459 Questions
How many feet per second does a car travel going 45 mph?
45 mph (5280 feet/1 mile)(1 hour/3600 seconds)
= 66 feet per second
Are seatbelts worn to protect passengers from speed or acceleration?
In a sense, yes. As a car accelerates, its passengers will also accelerate. As the passengers probably have less mass than the car, they accelerate differently to the car, which can cause their body to move quickly and suddenly (and may cause injury).
A seatbelt holds passengers in place in a car. As the car accelerates, passengers are restrained and cannot move greatly from their position in their seat, thus lowering the risk of injury.
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The above makes sense, but the seatbelts are more to protect from momentum, if you consider the first law of motion.
Momentum is p = mv (where p is momentum, m is mass and v is velocity). As a vehicle moves, according to the first law of motion, an object travelling at a certain state will continue to move in that state unless an external force acts upon it. Thusly, if you are riding in a vehicle and it is required to brake suddenly, the vehicle will stop, but your body - if it is not being impacted on by an external force such as a seatbelt - will continue to move forward with the same momentum which could possibly mean your body heading on its way through your windscreen.
(As a note, speed =/= velocity. Speed is a scalar quantity, whereas velocity is vector (has direction).)
When you combine the above response, and what was just written, you have your full answer.
Also, if you were wondering, seatbelts usually are both across the chest, and strapped across the hips because testing showed that one strap alone was not enough. Across the chest caused passengers to either slip out or caused decapitation, and across the waist/hips caused passengers' upper bodies to jerk forward (possible spinal damage, and damage to organs) in an accident. Thus, implementation of both allowed both bases to be covered effectively.
Acceleration is equal to the change in velocity over the change in time [a=(vf-vi)/(tf-ti).
a=(98m/s - 121 m/s)/(12s)=(-23m/s)/(12s)=-1.92m/s^2
That is completely unrealistic. C-14 has a half-life of several thousand years, not a few hours as implied in this example.
Anyway, to solve this in general you can write the exponential equation:
N = N0e-λt
where N is the remaining amount, N0 is the original amount, λ is the decay constant, and t is the time. Replace the numbers you know, and solve for λ. Note that the "disintegrations per minute" are proportional to the amount of remaining substance, so you can just as well assume that those numbers represent the remaining amount.
What is the formula of uniform acceleration?
There are several formulae that involve uniform acceleration. For example, the definition of uniform acceleration:dv/dt = c
or:
a = c
(where "c" is some constant).
How far do you travel at 10 mph in one second?
At 10 miles per hour, a car will travel 52800 feet in an hour. Divide by 60 minutes and the car will travel about 800 feet per minute or 14.66 feet per second.
How long will it take you to pass a passenger car at 60 mph without oncoming traffic?
1800 feet. NO! This is impossible to calculate without knowing the speed of each vehicle. Besides, the question asks 'how long' not 'how far', so the answer should be expressed in units of time, not distance. Also, if the passing vehicle must leave clearance before and after the pass (e.g. passing on a two lane road), the time and distance would increase. So this is wrong on several levels. I am further saddened by the fact that 15 people found this useful.
How will the distance in an object move be related to it's original potential energy?
If it is moved upward, it's potential energy will increase. If it is moved lower, then it's potential energy will decrease.
At the bottom, the car has kinetic energy of ½mv2. At the top, the car has kinetic energy of 0. If we ignore friction and wind resistance, the initial kinetic energy is converted to gravitational potential energy of mgh, where the m is again the mass of the car, g is the acceleration of gravity, and h is the vertical change in position of the car. Solving the two equations for h, we get
h=½v2/g=(0.5)(25 m/s)2/(9.8 m/s2)=31.888 m
To find the distance traveled along the road, we use a bit of trigonometry: sin(30°) = h/d = 0.5, so d = 2h = 63.776 meters
Of course, the actual value will be less, due to the friction and wind resistance that we ignored in our calculations.
It is approx 40 minutes and 3 seconds. The rate of descent is 22.5 feet per minute!
How fast does human hair grow in miles per hour?
The growth rate of human scalp hair is:
1/100000000 mph or 10^-8 mph.
Would a bullet ricochet on a steel target?
Yes, provided the target is not thin enough to be penetrated. You should shoot at paper targets in a designated shooting range.
Can the equation of kinetic energy of a gas be applied to a flame?
Yes, because kinetic energy is apart of the laws of physics, and can be applied anything that is in motion. Each molecule in the combustion process (that are in motion) are bound the laws of physics just as anything else in this world is. Therefore a flame must have kinetic energy, but in minuscule amounts.
All that heat and movement has generated 'static electricity' and you are earthing it.
Which of these has the most kinetic energy-?
These include very large things, like planets, and very small ones, like atoms. The heavier a thing is, and the faster it moves, the more kinetic energy it has.
The average speed of the train for the entire trip would be the harmonic mean of 60 mph and 40 mph. Using the formula for harmonic mean: 2 * 60 * 40 / (60 + 40) = 48 mph. So, the average speed of the train is 48 mph.
What is the formula for finding kinetic energy?
The formulae is: 1/2 x Mass (kg) x Velocity of object (m/s).
This problem can be solved using the pythagorean theorem
A2 + B2 = C2
A = 90 km/h
B = 50 km/h 902 + 502 = 10,600
√10,600 = 103.0
C = 103 km/h
