CELEN036
基础科学甲 Foundation Science A
Keys for Lectures 4-5: Free-body Diagrams, Energy, and Momentum-Neil
Mastering Physics 物理大师
that of maximum static friction, but Fg
remains the same.
is found using ∑F⃗ =Ma⃗
1.
1
𝑇 = 2 𝑚2 𝑎2
𝑇
𝑎1 = 𝑔 − 𝑚
1
𝑎2 = 𝑎1
2
1
𝑎2 = 4 𝑚2 𝑎1
𝑎1 =
𝑔
1+
7.
1
𝑚2
4𝑚1
𝑤
𝜇 = 𝑤𝐵
𝐴
𝑤 ×𝑔
|𝑎⃗| = 𝐵
2𝑤 +𝑤
𝐴
𝐵
Slowing down
8.
2.
157 N
𝐹=
𝑀𝑣02
2𝐿
281 lb
3.
TTFFTF
equal in magnitude but antiparallel to the
force on the earth due to the moon.
4.
the net force exerted on the car is zero.
the net force exerted on it is zero.
5.
9.
1
𝑊 = − 2 𝑘𝐿2
10.
8𝜇 2 𝑚𝑔2
𝑣2
11.
0.182 kg
0.164 J
0.167 J
the ramp, the puck, the Earth, and the spring
zero, at a maximum, and zero
zero, at a minimum, and at a maximum
203 N/m
∑𝐹𝑥 = 𝐹𝑝 cos 𝜃 − 𝐹𝑘 = 𝑚𝑎𝑥
∑𝐹𝑦 = 𝐹𝑁 − 𝐹𝐺 − 𝐹𝑝 sin 𝜃 = 𝑚𝑎𝑦
12.
0.378, 629
6.
The frictional force is always equal to μkn.
The frictional force is determined by other
forces on the objects so it can be either equal
to or less than μsn.
The force of kinetic friction is smaller than
1/2
CELEN036
基础科学甲 Foundation Science A
13.
14.
the disk, cart, and floor
1.8 m/s
42.3 kg ∙ m/s
38.07 J
1.2 m/s
-2.7%
-36%
15.
8.4 N ∙ s
Area
Area
Negative
-26 m/s
16.
𝑝 = 𝐹𝑡
𝑣=
𝐹𝑡
𝑚
𝑝2 = 𝐹Δ𝑡 + 𝑝1
𝑣2 =
𝐹Δ𝑡+𝑝1
𝑚
𝐽 = √5𝑚𝑣
1
26.6 degrees
𝑡=
√5𝑚𝑣
𝐹
43 m/s
2/2