Question

A 13kg kid is riding a skateboard down the street at 4 m/s. A 120kg granny steps in front of the kid on the skateboard and they collide. They stick together, if the granny's velocity was zero before the collision what is the velocity of their combined weight after they collide?

Answer 1

the velocity of their combined weight after they collide is 0.39 m/s

Step-by-step explanation:

From the information given, the kid and granny moved together after collision with a combined velocity. This means that the collision is inelastic. Given that momentum is conserved, for an inelastic collision, we would apply the formula;

m1u1 + m2u2 = (m1 + m2)V

where

m1 is the mass of the skateboard

v1 is the velocity of the skateboard

m2 is the mass of the granny

v2 is the velocity of the granny

V is the velocity of the combined weight

From the information given,

m1 = 13

u1 = 4

m2 = 120

u2 = 0(the granny was at rest)

By substituting these values into the formula, we have

13 x 4 + 120 x 0 = (13 + 120)V

52 = 133V

V = 52/133

V = 0.39 m/s