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Unformatted text preview: Solution for Long-answer Homework 6 Inertia and Momentum problems Solution to Long-answer Homework Problem 6.1() Problem: Two dogs are playing on an icy pond (you know eventually they are going to run into each other, right?). To the right is an xt graph of a collision between the two dogs . One dog has an inertia of 1kg (very similar to a standard cart). Dog 2 has inertia of 4kg . (a)What are the initial and final velocities of both dogs? (b)What are the changes in the velocities of both dogs? (c)Do these values satisfy equation 5 . 1 ? (d)Draw a vt graph for this collision. Does dog 1 ac- celerate? If so, when, and what is the sign of the acceleration? What about dog 2 ? t 1 (s) 2 (s) x ( t ) 5 (m)-3 (m) Dog 1 Dog 2 Collision (5,4) (m) Solution to Part (a) • V D 1 = x f − x i Δ t = 3m − ( − 3m) 1s = +6 m s • V D 1 f = x f − x i Δ t = − 1m − 3m 2s − 1 . 25s = − 4m . 75s =- 5 . 3 m s The method for finding Dog Two‘s velocities is the same: • V D 2 = 4m − 5m 1s =- 1 m s • V D 2 f = 5 . 4m − 4m 2s − 1 . 25s = 1 . 4m . 75s = 1 . 87 m s Grading Key: Part (a) 2 Points Solution to Part (b) Δ V D 1 = V D 1 f- V D 1 =- 5 . 3 m s- 6 m s =- 11 . 3 m s Δ V D 2 = V D 2 f- V D 2 = 1 . 87 m s- (- 1 m s ) = +2 . 87 m s Grading Key: Part (b) 2 Points Solution to Part (c) Eqt. 5 . 1 : M 2 M Std =- Δ V Std Δ V 2 4kg 1kg =-- 11 . 3 m s 2 . 87 m s 4 = 3 . 9 OK,OK it’s not true but it should be, the error is a product of rounding... Grading Key: Part (c) 1 Points 1 Solution to Part (d) Yes, both dogs accelerate (they each experienced a non-zero change in velocity, so this is true). Dog 1 accelerates in the negative direction during the instant of the collision, in the time interval of 1s to 1 . 25s (Dog 2 accelerates in the same time of course, and in the positive direction). v t 8 1 2 4 6 7 5 3 1s 1.25s 2s Dog 2 Dog 1 Grading Key: Part (d) 5 Points Total Points for Problem: 10 Points Solution to Long-answer Homework Problem 6.2(Momentous Events) Problem: One hot summer day, you are cruising on your 1000kg chopper at a velocity of 30 m s when a huge bug splatters on the visor of your helmet. Before its tragic death, the monstrousbug splatters on the visor of your helmet....
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