It takes the elevator in a skyscraper 4.0 s to reach its cruising speed of 10 m/s. A 60 kg passenger gets aboard on the ground floor. What is the passenger's weight (c) After the elevator reaches its cruising speed?

Video transcript

Hey, everyone. So this problem is dealing with forces. Let's see what it's asking us. An engineer tests an elevator during the test. It takes six, the, it takes the elevator six seconds to reach 14 m per second. He then places a 65 kg object in it. Find out how much the object weighs when the elevator is moving at m per second. Our multiple choice answers here are a newtons. B 441 newtons, C 637 newtons or D 345 newtons. So when we draw our, our free body diagram of the object, we have the weight acting in a negative Y direction and our normal force acting in a positive Y direction, we can recall from Newton's second law, but the sum of the forces is equal to the mass multiplied by the acceleration. Now, we are told that it takes the elevator six seconds to reach 14 m per second. But then once it is moving at that constant 14 m per second, we have a constant speed which means we have no acceleration. So when we have a constant speed acceleration is zero. So for this problem, this mass time, this mass multiplied by acceleration term is zero because some of the forces is the normal force in the positive direction minus the weight because that's in the negative direction. So we have the normal force minus weight equals zero. So when we add weight to both sides, we have the normal force equals weight. And we can recall that our weight is given by Mass multiplied by gravity. Now, the mass in this problem was told to us as 65 kg And gravity is a constant 9. m/s squared. We can plug that in to our calculator and get 637 Newtons is the weight of this object that aligns with answer choice C so C is the correct answer for this problem. That's all we have for this one. We'll see you in the next video.