跷跷板左边的公主和右边的门牙王一样重，这句话对么？
对
错
假如你是瓜店老板，遇到刘华强来买你的瓜，如果你在称重的时候将砝码偷偷向右移动会发生什么？
不知道
无事发生
赚大了！
If this object is moving at constant velocity, choose two correct condtions.
f=G and N=F
N=G and F=f
N=f and F=G
none of above
Assume the mass of object is m. If this object is accelerating to horizontal right with acceleration a, choose two correct condtions.
N=G and F-f=ma
N=G and F=f
N=G and f-F=ma
N-G=ma and F=f
Assume the mass of the object is 10kg. And the object only moves at horizontal direction. Calculate the normal force.（填空题全部不要带单位）
Assume the mass of the object is 10kg. And the coefficent of kinetic friction is 0.2(μ). Calculate the friction force at left.（填空题全部不要带单位）
（上一问摩擦力=20N）Assume the mass of the object is 10kg. And the acceleration of the object is 1 m/s2 to right. Calculate F.
In the below picture, normal is bigger or smaller than weight?
N(normal force)＜G(weight)
N(normal force)＞G(weight)
N(normal force)=G(weight)
condition is not enough
Calculate the Fpull component（分解的量） in y-direction.
F
F×cosθ
F×sinθ
F×tanθ
In y-direction, we can get which one of formula? (N=normal force, G=weight)
F×sinθ+G=N
N=F×sinθ
F×sinθ+N=G
N=G
Assume θ=30°，mass of object is 20kg, Fpull=200N. Calculate the normal force.
In x-direction, if the 20kg object moving to right with acceleration 5 m/s2. We can get which one formula?
F×cosθ+G=N
F×cosθ-f=100
F×cosθ=f
f-F×cosθ=100
（前置问题中支持力=100N），Assume θ=30°，mass of object is 20kg, Fpull=200N, acceleration to right=5m/s2. Calculate the coefficent of kinetic friction (μ).(结果保留一位小数)
If the object is slide downward（下滑）, which force cause this happen?
no force need
N
f
G
Draw the x and y direction are correct or incorrect?
x-direction is correct
x-direction is incorrect
x and y are all correct
x and y are all incorrect
calculate the component of weight in x-direction.
G×cosθ
G×sinθ
G×tanθ
G
calculate the component of weight in x-direction.
G×cosθ
G×sinθ
G×tanθ
G
F的力臂是多少？（m）填空题不要带单位
If this beam is balanced, What is the magnitude of F (N)? 填空题不要带单位
假如杠杆平衡，X为多少？（m）
50
100
150
200
这个图中哪个或哪些力可以使得杠杆顺时针（clockwise）旋转？
F
30
F和30
50
If this beam is balanced, What is the magnitude of F (N)?
35
14
28
25
40
20
（上一问F=28N）如果F=40N，请问此杠杆的运动状态？
clockwise
anti-clockwise
balance
cannot get answer
Which graph shows the best way to push the wheel to move?
a
b
c
d
请问向下的力F的力臂是多少？（m）
10
20
30
40
如果杠杆平衡，请求出F的大小