Question

Two ice skaters stand together as illustrated in Figure 3.28 (page 76). They push off and travel directly away from each other, the boy with a speed of 0.69 m/s. If the girl has a mass that is three fourths that of the boy, (a) What is the velocity of the girl? (+ is same direction as boy)

Answer 1

Given : v_b= 0.69 m /s ; m_g= (3/4)m_b

Solution :

According to the conservation of momentum :

P_initial = P_final

P_initial = m_bv_b + m_gv_g

Initially both are at rest , both velocities would be zero .

i.e. P_initial = 0

Now , P_final = m_bv_b+m_gv_g ( after )

By conservation equation ,

m_bv_b+m_gv_g = 0

m_bv_b = -m_gv_g

m_b(0.69 m/s)= -(3/4)m_bv_g

v_g = -0.69×4/3

= -0.92 m/s .

Hence velocity of girl is (-0.92 m/s) . Negative sign indicates that direcation of girl's velocity is opposite to that of boy.