# physics question/explanation - projectile motion vs. inclined plane

#### nexus6

10+ Year Member
7+ Year Member
Could someone explain this to me? I've tried to use logic but haven't figured it out:

In projectile motion, the horizontal component can be calculated using cos(theta). However, on an inclined plane, the horizontal component is calculated using mgsin(theta). Why sin and not cos? Thanks.

#### physics junkie

10+ Year Member
5+ Year Member
Could someone explain this to me? I've tried to use logic but haven't figured it out:

In projectile motion, the horizontal component can be calculated using cos(theta). However, on an inclined plane, the horizontal component is calculated using mgsin(theta). Why sin and not cos? Thanks.

Could someone explain this to me? I've tried to use logic but haven't figured it out:

In projectile motion, the horizontal component can be calculated using cos(theta). However, on an inclined plane, the horizontal component is calculated using mgsin(theta). Why sin and not cos? Thanks. Its kind of hard to see why the angles are the same. My advice is to think about it or memorize it. Oh, and you can ignore the axes...they don't matter since the geometry is independent of the coordinate system.

try: http://images.google.com/images?hl=en&client=firefox-a&rls=org.mozilla:en-US:official&q=inclined%20plane box sine&um=1&ie=UTF-8&sa=N&tab=wi for other diagrams.

For how many people struggle with this I'm surprised there is no explanation of the geometry online.