What is the power output of an engine when a car of mass M accelerates with the constant power from rest to a final speed V over a distance d on flat, level ground?
Ignore
energy lost due to friction and air resistance.
Derive a formula for the power P in terms of variables: the mass M, the final speed V, and the distance d.
P=P(M,V,d) ?
Derive a formula for the power P in terms of variables: the mass M, the final speed V, and the distance d.
P=P(M,V,d) ?
v=v(t)
The speed is a function of time.
Pt
= ½m v(t)²
Because of the energy conservation law.
v(t)²=2tP/m=(2P/m)t
v(t)=(2P/m)½t½
x(t)=(2P/m)½
(⅔t3/2)
x(t)²=(2P/m)
(⅔)²
t³
t=v(t)²
/ (2P/m)
t³=v(t)⁶
/ (2P/m)³
x(t)²=(2P/m)
(⅔)²
t³=(2P/m)
(⅔)²
v(t)⁶
/ (2P/m)³
x(t)²=(⅔)²
v(t)⁶
/ (2P/m)
²
x(t)=(⅔)
v(t)³
/ (2P/m)
2P/m
= (⅔) v(t)³
/ x(t)
P
= ½(⅔) v(t)³m
/ x(t)
P
= ⅓ v(t)³m
/ x(t)
= ⅓ V³m
/ d
No comments:
Post a Comment