two force P and Q have a resultant force R with a max value of 60N and a minimum value of 10N. Find R if the angle between P and Q is 40 degrees

P,Q,R係vector黎

希望得到高人解答

AP42 :two force P and Q have a resultant force R with a max value of 60N and a minimum value of 10N. Find R if the angle between P and Q is 40 degrees

P,Q,R係vector黎

希望得到高人解答 :oops:

一件object有兩支force act on佢
最大net force出現o係兩支force parallel 向住同一方向
最細net force出現o係兩支force係exactly opposite direction
maximum force 60N = P+Q
minimum force 10N = P-Q
=>P=35N，Q=25N

之後點做，要諗諗先

Cosine law:
R² = P² + Q² -2PQcos140°

Another derivation:
Bold fonts denote vectors.
R = P + Q
Square of magnitude of R = (P + Q)·(P + Q)

KMB59 :Cosine law:
R² = P² + Q² -2PQcos140°

Another derivation:
Bold fonts denote vectors.
R = P + Q
Square of magnitude of R = (P + Q)·(P + Q)

請問點解係140? banghead

AP42 :請問點解係140°? banghead

如P、Q和R是三角型的邊，則P與Q的夾角是180°減40°。
另外2P·Q
= 2PQcos40°
= -2PQcos(180° - 40°)