Question

求下面高中物理题答案 有关能量守恒的

I push a cart up with a constant force up a slope to a height of 1/4 meter. The mass of the cart is 1/4 kg. The cart moves 1/2 meter along the table as I do this. After I let it go, the cart continues up the slope
until it reaches a height of 1/2 meter and then starts back down. What was the magnitude of the force with which I pushed the cart?
答案2.45/√5 、
要计算过程和步骤

Answer 1

翻译 我用恒力将一辆车推上高1/4米的斜坡.小车的质量是1/4千克.当我这样做的时候小车在斜面上移动了1/2米.小车继续在斜面上滑行.直到小车到达1/2米的高度时开始返回.求我对小车施加的力是多少牛.
有两种解法.
一.根据机械能守恒得.F*S=mg*h 其中S=0.5m mg=5/2N h=1/2m
所以解得F=5/2N
二.由高1/4米,长1/2米得斜面倾斜角为30度.2*(F-mg/2)/m*L=g/2*2*L 因为前后两过程的末速度相同.
解得F=5/2N
上面的解答是当斜面的摩擦因素为零时的答案
若斜面粗糙的话,那么摩擦力大于零小于5/2N所以答案为 5/2N<F<5N

Answer 2

slope with zero frictional coefficient?

Answer 3

摩擦系数为0， 则： f=m*(gh)^0.5, h=1/2, 带入可得

Answer 4

123456

Answer 5

2.5