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Chapter 4-4 Worksheet Applications of Newton’s 2nd Law Name Period Make sure your notes are complete for this material! If you get stuck, look at Chapter 4 in your book. Make sure to read what is in italics- They are hints! What do the variables in the above equation mean and what units are they in? F= m= a= 1st Application of F= ma: Use with One-Dimensional Motion equations 1) A 6-lb mallard is trying to land on a frozen pond. The duck hits the ice going 15 m/s. It eventually stops sliding after 20 meters on the ice. Calculate the force of friction that stopped him. Do you remember how many pounds are in a kilogram? You should… calculate the acceleration from a 1-D Motion equation and then you can use F= ma to find the force. Why is the answer negative? 2nd Application of F= ma: to find an object’s weight 2) If Sam weighs 160 lbs., calculate his weight in Newtons on earth. (Don’t forget 1kg = 2.2 lbs.) Find his weight on the moon in Newtons where gravity is 1/6th of what it is on the earth. 3rd Application of F= ma: or when there are 2 accelerations in the y-direction: 3) We can also use F = ma if there are other accelerations acting in the vertical direction besides the acceleration due to gravity. The equation becomes F = m (9.8 m/s2 + a) a = the other acceleration in m/s2 a = positive when the object is ___________________ a = negative when the object is ___________________ You lift a bag of groceries (mass 20 kg) off the floor with an acceleration of 5 m/s2. If the bag handle can withstand a tension of 250 N, will the bag break if you lift it with that acceleration? (To solve this all you do is add the acceleration to the acceleration due to gravity.) 4th Application of F= ma: to find g forces This part is not in your book. We are adding it. A g-force is how many times your weight you are experiencing. Sitting here, filing out this very exciting worksheet, you are experiencing one g. At the bottom of a rollercoaster, you feel heavier, you can be experiencing 2 to 5 g’s. At the top of those little hills near the end of the rollercoaster, you feel lighter as you fly out of your seat. This means you are experiencing less than one g. These are often called negative g’s even though they are not negative numbers, just decimals. Humans typically blackout around 7 to 8 g’s. 4) a) Explain what it means to feel 2 g’s. _________________________________________________________ b) Explain what it means to feel 0.5 g’s. ________________________________________________________ c) Calculate one g for you. (F.Y.I. One g is the same as your weight in Newtons.) d) If you weigh 400 N and you experience 1,200 N of force, how many g’s would that be for you? e) So, what is the formula for the number of g’s experienced? # of g’s = 5) You (mass 50 kg) and your friend (mass 60 kg) experience 1,200 N of force at the bottom of the hill on the Wild Thing. How many g’s is this for you and for your friend? Now try these problems on a separate sheet to make sure you understand this material. 6) Jeff Gordon (170 lbs) initially traveling at 98 mph hits a wall with his car and comes to a complete stop in 0.70 seconds. Find the number of g’s Jeff Gordon would experience in the crash. (ans. 6.4 g’s) 7) You (mass 70 kg) are riding in an elevator. It accelerates upward at 1.2 m/s2 and then it decelerates at the top at 0.9 m/s2. Find what the scale will read in pounds, and how many g’s you are experiencing a) when you are at rest before the elevator moves. (ans. 154 lbs, 1 g) b)when you accelerate on the way up. (ans. 173 lbs, 1.12 g’s) c) when you are decelerating at the top. (ans. 140 lbs, 0.91 g) (Answer these on a separate sheet.)