As in an element?
He/ Helium
Answer:
when all forces acting on an object remain the same
4. The answer is that you will see the same sights as when you are resting. That is because you and mirror are in rest one relative another. If your relative speed is 0, it doesn't matter how quickly you both travel in relation to other objects.
5. The relativistic effects will not alter if the speed of light is reduced to 50m/s. According to the principle of constancy (2nd postulate), the upper limit of speed is 50m/s, which will be impossible for material objects to achieve because as the speed of light decreases, the sizes of humans and all other materials decrease as well, decreasing our relativistic velocity and thus making c=50m/s unattainable for material objects, and thus the relativistic effects will remain unchanged. A pedestrian must use caution when crossing the roadway. Let's assume you see a car arriving at 60 kilometers per hour, or 16.666 meters per second, from a distance of 100 meters. It'll take 6 seconds to arrive, giving you plenty of time to cross the street. Because the light reflected from the car to your eyes left the car two seconds ago, the car will reach at your location in four seconds and hit you (if the car is travelling in the lane on the far side of the road). It looks to you that approaching automobiles traveling at the legal limit are traveling at a speed of 100 / 4 = 25 m/s, which is 50% faster than the genuine speed of 16.666 m/s. When considering whether or not it is safe to cross the road, one would quickly become accustomed to this.
6.
Answer:
Doppler effect changes the wavelength of the light emitted, depending upon whether source is moving away or coming towards the observer(detector).
Explanation:
Doppler effect in light is actually a relativistic effect but somewhat similar to the one which happens in sound waves.
When the source is moving away from the detector, the wavelength of the light emitted from the source appears to be increased as seen by the detector, as a result the frequency decreases(we know that frequency of light= speed of light/wavelength of light. Here speed of light is constant and frequency of light is inversely proportional to its wavelength)
Due to this decrease in frequency the light emitted from the source appears more red, since red color is on low frequency side in the electromagnetic spectrum.
Similarly for the source moving towards the detector, the wavelength appears to be decreased, thereby resulting in increase in frequency and the source appears blue. The shift in frequency is known as doppler shift.
The shift in frequency when the source is moving away is known as redshift and the one where the source is moving towards detector is known as blueshift
Answer:
D. 2
Explanation:
The skydiver will reach terminal velocity when gravity = air resistance. When this occurs, he/she will no longer accelerate and his/her speed will be constant.
Once the skydiver opens the parachute, his/her speed will decrease suddenly, and again the air resistance increases due to the parachute's large area. Eventually, gravity will equal air resistance again and terminal velocity will be reached for the second time.
Even though the speeds are different, the first terminal velocity is much higher than the second one, this question refers to how many times terminal velocity is reached, not how many times the skydiver accelerates.