+0

# Momentum and Its Conservation

0
199
2

A 62.0 kg child is sitting in a wagon full of bricks. The wagon and all of the bricks together have mass of 150. kg. In order to move the wagon east without touching the ground, the child throws two bricks, each of mass 3.00 kg, westward at 2.00 m/s. What is the new velocity of the child, wagon, and remaining bricks

physics
Guest Jan 25, 2015

#2
+26550
+5

Anonymous is correct, but just to flesh it out a little:

Momentum is conserved (assuming no friction etc.) so:

Initial momentum = 0

Final momentum of wagon + child after bricks are thrown = (62 + 150 - 6)*velocity

Final momentum of bricks = -6*2  (assuming velocity is negative to the west and positive to the east)

(62+150-6)*velocity - 6*2 = 0

velocity = 6*2/(62+150-6) m/s

$${\mathtt{velocity}} = {\frac{{\mathtt{6}}{\mathtt{\,\times\,}}{\mathtt{2}}}{\left({\mathtt{62}}{\mathtt{\,\small\textbf+\,}}{\mathtt{150}}{\mathtt{\,-\,}}{\mathtt{6}}\right)}} \Rightarrow {\mathtt{velocity}} = {\mathtt{0.058\: \!252\: \!427\: \!184\: \!466}}$$

or velocity ≈ 0.058 m/s

.

Alan  Jan 26, 2015
Sort:

#1
+5

$$\left({\mathtt{3}}{\mathtt{\,\small\textbf+\,}}{\mathtt{3}}\right){\mathtt{\,\times\,}}{\mathtt{2}} = {\mathtt{12}}$$

$${\mathtt{150}}{\mathtt{\,-\,}}{\mathtt{3}}{\mathtt{\,-\,}}{\mathtt{3}}{\mathtt{\,\small\textbf+\,}}{\mathtt{62}} = {\mathtt{206}}$$

$${\mathtt{206}}{V} = {\mathtt{12}}$$

$${\mathtt{V}} = {\frac{{\mathtt{12}}}{{\mathtt{206}}}}$$ m.s-1

Guest Jan 26, 2015
#2
+26550
+5

Anonymous is correct, but just to flesh it out a little:

Momentum is conserved (assuming no friction etc.) so:

Initial momentum = 0

Final momentum of wagon + child after bricks are thrown = (62 + 150 - 6)*velocity

Final momentum of bricks = -6*2  (assuming velocity is negative to the west and positive to the east)

(62+150-6)*velocity - 6*2 = 0

velocity = 6*2/(62+150-6) m/s

$${\mathtt{velocity}} = {\frac{{\mathtt{6}}{\mathtt{\,\times\,}}{\mathtt{2}}}{\left({\mathtt{62}}{\mathtt{\,\small\textbf+\,}}{\mathtt{150}}{\mathtt{\,-\,}}{\mathtt{6}}\right)}} \Rightarrow {\mathtt{velocity}} = {\mathtt{0.058\: \!252\: \!427\: \!184\: \!466}}$$

or velocity ≈ 0.058 m/s

.

Alan  Jan 26, 2015

### 14 Online Users

We use cookies to personalise content and ads, to provide social media features and to analyse our traffic. We also share information about your use of our site with our social media, advertising and analytics partners.  See details