force, mass and momentum

[amy]

A skateboarder with a total mass of 70 kg starts from rest at the top of a ramp and accelerates down it. The ramp is 25 m long and is at an angle of 20⁰ to the horizontal. The skateboarder has a velocity of 12.2 m s^–1 at the bottom of the ramp.

(i) Calculate the average acceleration of the skateboarder on the ramp.

(ii) Calculate the component of the skateboarder’s weight that is parallel to the ramp.

 

 

using one of the equations of motion i can get the acceleration to be 2.98 ms^-2

but i,m having trouble with the second part , i know that the vertical component (his weight due to gravity) is (70)(9.8) = 686N.

can i use trigonometry or something to get the the component parallel to the ramp?

Edited March 13, 2013 by amy

[swansont]

A skateboarder with a total mass of 70 kg starts from rest at the top of a ramp and accelerates down it. The ramp is 25 m long and is at an angle of 20⁰ to the horizontal. The skateboarder has a velocity of 12.2 m s^–1 at the bottom of the ramp.

(i) Calculate the average acceleration of the skateboarder on the ramp.

(ii) Calculate the component of the skateboarder’s weight that is parallel to the ramp.

 

 

using one of the equations of motion i can get the acceleration to be 2.98 ms^-2

but i,m having trouble with the second part , i know that the vertical component (his weight due to gravity) is (70)(9.8) = 686N.

can i use trigonometry or something to get the the component parallel to the ramp?

 

There is a parallel component, perpendicular component, and the resultant. Trig can indeed give you relationship between the three.

[Tim the plumber]

Draw a diagram of the skate boarder on the ramp.

 

Draw on it the forces, start with gravity acting down.

 

The reaction of the ramp against the wheels of the skate board will not be vertical but straight away from the ramp.

 

When you have done this the answer will be obvious.(ish)