Newton’s 2nd Law Problems



Newton’s 2nd Law ProblemsUntil now, we have been working to describe motion, which is a branch of physics called kinematics: the study of motion. Now it’s time to consider the causes of motion, which is a branch called dynamics: the study of forces. Newton’s 2nd Law is ground zero for dynamics. Let’s start with a dramatic example.-6858096520001. The most powerful machine ever built was the Saturn V rocket, which landed 12 Americans on the moon. It had a launch mass of 2.80 million kg, a weight of 27.4 million N (6.20 million pounds) a thrust of 34.0 million N (7.65 million pounds) and a height of 111 m (363 ft.) A) Find Fnet on the Saturn V immediately after launch. Sketch and label the forces.B) Find the acceleration of the Saturn V immediately after launch.C) How fast was the Saturn V going when it cleared the tower? Assume the tower is the same height as the rocket, and that the acceleration is constant for this part of its flight. Sketch it!D) How do you think that the fact that the rocket was burning fuel at a rate of 14 thousand kg/s would affect your speed in C) above? Do you think the acceleration was really constant?2. You come across a sealed metal box on a frozen lake. (Assume there is no friction between the ice and the box.) A) You want to find out what its mass is, but it is too heavy to lift. Instead, you push on it with a force of 120 N, and measure its acceleration to be 0.25 m/s2. What is its mass? Sketch it. Remember, algebra first, before you plug in any #’s.B) A bad person tries to take the box you found away from you. They push with a force of 244 N due north. You push due south but the box still accelerates north with an acceleration of 0.050 m/s2. How hard are you pushing now? Assume the box has the same mass you found in part A). Sketch it. Remember, Newton’s 2nd Law is really Fnet = ma, not just F = ma! Algebra first. ................
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