Laws Of Motion Question 431

Question: A particle moves in the xy plane under the action of a force F such that the value of its linear momentum P at any time t is Px=2cost,

Py=2sint . The angle θ between F and P at a given time t will be

Options:

A) 90

B) 0

C) 180

D) 30

Show Answer

Answer:

Correct Answer: A

Solution:

[a] P=Px2+Py2=(2cost)2+(2sint)2=2

If m is the mass of the body, then kinetic energy =P22m=(2)22m=2m

Since kinetic energy does not change with time, both work done and power are zero. Now, power =Fvcosθ=0 As F0,v0

cosθ=0 orθ=90

As direction of p is same that of v,

(P=mv), hence angle between F

and P is equal to 90 .



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