Question

Grandma Sue (mass 80 kg) and her grandson James (mass 40 kg) are on a smooth icy surface. As Grandma Sue whizzes around the icy surface at 3 m/s in a straight line, she is suddenly confronted with scared James standing at rest directly in her path. Rather than knock him over, she picks him up and continues her uniform motion in a straight line without braking. Find the speed of Grandma Sue and James after the collision.

Answer 1

v = 2 m/s

Step-by-step explanation:

Here, we will use the law of conservation of momentum to solve this problem:

`m_1u_1 + m_2u_2 = m_1v_1+m_2v_2`

where,

m₁ = mass of grandma = 80 kg

m₂ = mass of James = 40 kg

u₁ = initial speed of grandma = 3 m/s

u₂ = initial speed of James = 0 m/s

v₁ = v₂ = v = final speed of grandm and James = ?

Therefore,

`(80\ kg)(3\ m/s)+(40\ kg)(0\ m/s)=(80\ kg)(v)+(40\ kg)(v)\\\\(120\ kg)v = 240\ Ns\\\\v = (240\ N.s)/(120\ kg)\\`

v = 2 m/s