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Questions in physics

[Done] Thirty years ago, police would check a highway for speeders by sending a helicopter up in the air and observing the time it would take for a car to travel a marked distance. If a car was observed to take 7.2 seconds to travel this distance, how much time did it take the car to travel the same distance in hours?

[Done] What happens to the density of a given substance if you increase the amount of the substance that you have?

[Done] How do you convert kilograms (kg) to newtons (N)?

[Done] How can there be so many different substances in the world if there are only a few common elements?

[Done] Calculate the magnitude of the horizontal component of a vector that is 100 units long and oriented at 45 degrees.

[Done] How do you find acceleration from net force?

[Done] When is there zero net force on an object?

[Done] How much energy do you save per hour if you replace a 60-watt lightbulb with a 55-watt lightbulb?

[Done] Which of the following is NOT an example of accelerated motion? A. an airplane taking off down a straight runway B. a boulder falling off a cliff in a straight path C. a ball being thrown straight up D. a bicyclist moving in a straight line at a constant speed

[Done] A guitar string vibrates with a frequency of 256 Hz. What is the period of vibration?