During a snowball fight two balls with masses of 0.30 and 0.70 kg,respectively,are thrown in such a manner that they meet head-on and combine to form a single mass.The magnitude of initial velocity for each is 12.0 m/s.What is the speed of the 1.0-kg mass immediately after collision?
A)zero
B)4.8 m/s
C)12 m/s
D)8.4 m/s
E)3.6 m/s

Question

Quizplus · Accepted Answer

Momentum is conserved in the collision, so the total momentum before the collision is equal to the total momentum after the collision. The total momentum before the collision is:$$p_i = m_1v_1 + m_2v_2 = (0.30 	ext{ kg})(12.0 	ext{ m/s}) + (0.70 	ext{ kg})(12.0 	ext{ m/s}) = 12.0 	ext{ kg m/s}$$The total momentum after the collision is:$$p_f = (m_1 + m_2)v_f = (0.30 	ext{ kg} + 0.70 	ext{ kg})v_f = 1.0 	ext{ kg}v_f$$Setting the initial and final momenta equal to each other, we get:$$p_i = p_f$$$$12.0 	ext{ kg m/s} = 1.0 	ext{ kg}v_f$$Solving for $v_f$, we get:$$v_f = \frac{12.0 	ext{ kg m/s}}{1.0 	ext{ kg}} = 12.0 	ext{ m/s}$$Therefore, the speed of the 1.0-kg mass immediately after the collision is 12.0 m/s.

During a Snowball Fight Two Balls with Masses of 0