p
Lv 4
p asked in Science & MathematicsPhysics · 9 years ago

Another physics K**LER prob?

A crate (A) of 13 kg on a frictionless inclined plane is attached to another crate (B) of 22 kg by a massless rope. The rope passes over an ideal pulley so that B is suspended in air. The plane is inclined at θ = 24.0°. Use conservation of energy to find how fast B is moving if after A has moved 1.4 m along the incline , starting from rest.

okay, this question has a picture that really doesn't give much info. It is a right triangle, A is on the hypotenuse, B is on the opposite or (vertical 90°), & θ = 24.0°.

the ans is roughly around 3.62 m/s, help me get to it

thanks

Relevance
• DH
Lv 7
9 years ago

Use conservation of energy

(K + U)1 = (K + U)2

K1 = 0 and U1 = 0 (Set the initial position of each block to 0)

Now U2 = mA*g*1.4*sin(24) - mB*g*1.4 and K2 = 1/2*mA*v^2 + 1/2*mB*v^2

so 1/2*mA*v^2 + 1/2*mB*v^2 + mA*g*1.4*sin(24) - mB*g*1.4 = 0

so v = sqrt(2*( mB*g*1.4 - mA*g*1.4*sin(24))/(mA + mB)) =

v = sqrt(2*(22*9.8*1.4 - 13*9.8*1.4*sin(24))/(13 + 22)) = 3.62m/s