An astronomy class is so excited by the discovery of planets around other stars that they decide to do a library exhibit on the subject so that everyone in the school can learn about it. In this exhibit they want to pay tribute to both the astronomers of today who have done the work AND some of the scientists of the past whose work was essential to making the discoveries possible (and directly related to the techniques involved). Which of the following scientists of the past should definitely be included in the exhibit? a. George Herbigâ
b. Ejnar Hertzsprungâ
c. Ptolemyâ
d. Gerard Kuiperâ
e. Christian Dopplerâ

Iwould say a is accurate

Is this multiple choice question

Your answer would be b. the total kinetic and potential energies of its particles 

Part a:   using momentum conservation we have:   direction x:   (15) (7.0) + 0 = (15) (4.2) cos (-20 °) + (10) v₂ (f) cosθ  (10) v₂ (f) cosθ = (15) (7.0) - (15) (4.2) cos (-20 °) (eq 1)  direction y:   0 + 0 = (15) (4.2) sin (-20 °) + (10) v₂ (f) sinθ  (10) v₂ (f) sinθ = - (15) (4.2) sin (-20 °) (eq 2)  we divide both equations (1) and (2):   left side:   (10) v₂ (f) sinθ / (10) v₂ (f) cosθ = tanθ  right side:   - (15) (4.2) sin (-20 °) / (15) (7.0) - (15) (4.2) cos (-20 °)  clearing the angle we have:   θ = tan⁻¹ [- (15) (4.2) sin (-20 °) / (15) (7.0) - (15) (4.2) cos (-20 °)]  θ = 25 °  we use any of the equations to find the speed.  from (2) we have:   (10) v₂ (f) sinθ = - (15) (4.2) sin (-20 °)  v₂ = - (15) (4.2) sin (-20 °) / (10) sin25 °  answer:   v₂ = 5.1m / s  note:     θ = 25 ° (direction is in the first quadrant, north of east)  part b:   initial kinetic energy:   k (i) = 0.5 (15) (7.0) ²  = 370j (rounded)  final kinetic energy:   ke (f) = 0.5 (15kg) (4.2m / s) ² + 0.5 (10kg) (5.1m / s) ²  = 260j (rounded)  answer:     a difference of 110j, so it was an inelastic collision.