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Download Newton`s 2nd Law Key - Northwest ISD Moodle
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Name Date Pd Net Force Particle Model Worksheet 2: Newton's 2nd Law 1. A 4600 kg helicopter accelerates upward at 2.0 m/s2. Determine the lift force exerted on the propellers by the air. Make a quantitative force diagram. Write a net force equation for the axis along which forces are not balanced. y Flift Fnet x Fg Fnet ma Flift Fg ma Flift ma Fg N Flift 4600kg 2.0 sm2 (4600kg 10 kg ) 55,200N 2. The maximum force that a grocery bag can withstand without ripping is 250 N. Suppose that the bag is filled with 20 kg of groceries and lifted with an acceleration of 5.0 m/s2. Do the groceries stay in the bag? Make a quantitative force diagram. Write a net force equation for the axis along which forces are not balanced. Bag rips y Fnet Fnet ma FN,groceries,bag bottom FN Fg ma FN 200N 20kg 5.0 sm2 x FN 300N Fg, groceries,earth The bag would have to provide a 300N force on the groceries to produce this acceleration. The 300N force provided by the groceries on the bag are greater than the 250 N limit. The bag rips. ©Modeling Instruction 2013 1 U5 Net Force – ws2 v3.1 end 3. A student, standing on a scale in an elevator at rest, sees that his weight is 840 N. As the elevator rises, the scale reading increases to 1050 N, then returns to normal. When the elevator slows to a stop at the 10th floor, the scale reading drops to 588 N, then returns to normal. Draw a motion map for the student during his elevator ride. Determine the v acceleration at the beginning and end of the trip. Make quantitative force diagrams. Write a net force equation for the axis along which forces are not balanced. a=0 y v y FN Fnet FN Fnet end a=0 v x x a v v a v v a Fg Fg v a a start start Starting up a Slowing to a stop The scale reads the normal force acting on the student. W = Fg = –840N Fnet a m FN Fg Fnet a m FN Fg a m m 1050 840N a 2.5 s 84kg s a m m 588 840N a 3.0 s 84kg s When the scale reads 840 N, the net force on the student = 0, so velocity is constant. 4. A sign in an elevator states that the maximum occupancy is 20 persons. Suppose that the safety engineers assume the mass of the average rider is 75 kg. The elevator itself has a mass of 500 kg. The cable supporting the elevator can tolerate a maximum force of 30, 000 N. What is the greatest acceleration that the elevator's motor can produce without snapping the cable? Make a quantitative force diagram. Write a net force equation for the axis along which forces are not balanced. y Fnet Fnet a m FT Fg x a m m 30,000N 20,000N a 5.0 s 2000kg s Fg ©Modeling Instruction 2013 N Fg 20 75kg 500kg 10 kg 20,000N FT 2 U5 Net Force – ws2 v3.1