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100% Tue 5:26 PM a E Chrome File Edit View History Bookmarks People Window Help Chapter Summary SG 7-8 work andEx C lis H8INeed Help x 3: A Healing Touch M x g erext x myBLINN inn Cox SG 9 Impulse and Steven C Secure https mp A My Home College Physics PHYS Steven Carpenter Course I Content I Dropbox l Progress l Resources v I Tools v Unit 2 dom Table of Contents SG 9 Impulse and Momentum SG 9 Impulse and Momentum 200kg H3. Jack and John are riding bumper cars. Given m1 100kg for jobs Before the collision, 4.0 m/se 8.0 m/s izt 5.0 m/s 2.0 m/s After the collision Jack has velocity i51 4.0 m/s 5.0 m/s) a) Find John's final velocity, v2f Hint: there will be an x and a y part b) What percent of kinetic energy was lost in the collision? c) Is the collision elastic, totally in elastic, or partially inelastic? Show proof ATE STAFF H4. Crash Smarties: Crash statistics show that it is safer to be riding in a heavy car in an accident than in a light car JOBS Let's test this theory, using a typical SUV mu 2500kg, and a small economy car: mc 1500kg, Standard crash tests occur at 35 mi/h, so we'll let the initial speed be vo 15 m/s Assume a SUV and a car collide head-on in a totally inelastic collision. m J ms, v, vo, and m2 mc, v2 -vo a) Find the final velocity symbolically (letters only), then plug in values the values to get a final result b) found from Av crash Find of each vehicle Acceleration can be aav Assume the takes 0.10 s. the acceleration Which vehicle suffered more severe accelerations? udionote c) Let's test the damage done to the cars. As the cars collide the hoods of the cars collapse. We'll assume model this with collapse with a single spring of spring constant k 1x10 N/m. (In truth the spring constants change as the hoods collapse. Also the hoods would have different spring constants, we have assumed they collapse as a single unit.) Use the speeds computed above to find the compression of the hood (spring). Find the solution symbolically, then plug DOCX in the values to get a result. namesakes In an elastic collision, the final kinetic energy is equal to the initial kinetic energy.

Explanation / Answer

H3:

a)

using conservation of momentum

m1 v1i + m2 v2i = m1 v1f + m2 v2f

(100) (4x + 8y) + (200) (- 5x + 2y) = (100) (4x + 5y)+ (200) v2f

400x + 800y - 1000x + 400y = 400x + 500y + (200) v2f

400x + 800y - 1000x + 400y - 400x - 500y = (200) v2f

- 1000x + 700y = (200) v2f

v2f = -5x + 3.5y

b)

|v1i| = initial speed of m1 = sqrt(42 + 82) = 8.94 m/s

|v2i| = initial speed of m2 = sqrt((-5)2 + 22) = 5.4 m/s

|v1f| = final speed of m1 = sqrt(42 + 52) = 6.4 m/s

|v2f| =final speed of m2 = sqrt((-5)2 + 3.52) = 6.1m/s

KEi = initial total KE = (0.5) (m1 v1i2 + m2 v2i2) = (0.5) ((100) (8.94)2 + (200) (5.4)2) = 6912.2 J

KEf = final total KE = (0.5) (m1 v1f2 + m2 v2f2) = (0.5) ((100) (6.4)2 + (200) (6.1)2) = 5769 J

Loss = KEi - KEf = 6912.2 - 5769 = 1143.2 J

%age loss = Loss x 100/KEi = 1143.2 x 100/6912.2 = 16.54%

c)

the collision is partially inelastic since the kinetic energy before and after the collision are not same which is one of the condition for inelastic collision. this is partial since the bullet and bob do not share the same speed after collision which is another condition for totally inelastic collision.

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