Which is A student weighing 45kg runs down a slope and suddenly jumps with a speed of 3 m s onto a stationary skateboard The student and the skateboard move with a velocity of 2.7 m s What is the mass?

Answer 1

This can be modeled as a "collision" where momentum is conserved. Momentum equals mass times velocity (p = mv).

Let's call the momentum of the student before the collision ps0 and the momentum of the skateboard before the collision pb0. Let's call the momentums after the collision ps1 and bs1.

Since momentum is conserved, ps0 + pb0 = ps1 + bs1. Plugging the numbers for the momentum gives us:

(45)(3) + (m)(0) = (45)(2.7) + (2.7)(m), where m is the mass of the skateboard.

Simplified:

135 = 2.7m + 121.5

13.5 = 2.7m

m = 5

So the mass of the skateboard is 5 kg.

(Note that the units are all in kilograms, meters, and seconds they call match up in the calculations.)