A girl of mass 40 kg jumps with a horizontal velocity of 5 m/s on to a stationary cart with frictionless wheels. The mass of cart is 3 kg, what is her velocity as the cart start moving?

m_g=40kg

u_g=5ms^-1

m_c=3kg

u_c=0

v_b=v_c=x(Let)

By conservation of momentum,

P_i=P_f

or, m_g x u_g + m_c x u_c = m_g x v_g + m_c x v_c

or, 40kg x 5ms^-1 + 3kg x 0 = 40kg x v + 3kg x v

or, 200 kgms^-1 + 0 = v(40kg+3kg)

or, 200kgms^-1 = v x 70kg

so, v = 200/70 m/s

         = 20/7 ms^-1

         = 2.857ms^-1

          = 2.86ms^-1