You are standing at rest on a 4.1-kg stationary skateboard talking to your favor

Question

You are standing at rest on a 4.1-kg stationary skateboard talking to your favorite brick.
The brick says something you don't like so you throw it straight forward at a speed of 13.0 m/s.
Your mass is 55.0 kg, and that of the brick is 2.5 kg. You can ignore friction
between the skateboard and the (level) ground.

(a) What is the initial momentum of the system of you, the skateboard and the brick?

psys =  kg·m/s

(b) What is the final momentum of the system of you, the skateboard and the brick?

psys =  kg·m/s

(c) How fast and in what direction do you and the skateboard move after you throw the brick?

m/s  ---Select--- forward backward

(d) The system's  ---Select--- total mechanical internal kinetic potential energy was conserved but its  ---Select--- total mechanical internal kinetic potential energy was NOT.

Explanation / Answer

a) as body is rest initially momentum is =mass x velocity =2.5 x 13 =32.5kgm/s

b)final momentum = zero as bodies comes to rest

c)total mass of body and skateboard = 55+4.1 =59.1kg

59.1 x v =2.5 x 13

v=0.56 opposite to the direction of stone

d)internal kinetic energy

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