Motion In Two Dimension(11th And 12th > Physics ) Questions and Answers
Explanation:-
Answer: Option B. -> t1t2 α R:
B
For same range angles of projection should be θ and 90 - θ
So, time of flights t1 = 2usinθg and
t2 = 2usin(90−θ)g = 2ucosθg
By multiplying = t1t2 = 4u2sinθcosθg2
t1t2 = 2g (u2sin2θ)g = 2Rg ⇒ t1t2 α R
Explanation:-
Answer: Option C. -> √v2+g2t2−(2vsinθ)gt:
C
Instantaeous speed of rising mass after t sec will be vt = √vx2+vy2
where vx = v sin θ = Horizontal component of velocity
vy = v sin θ - gt = Vertical component of velocity
vt = √(vcosθ)2+(vsinθ−gt)2
A stone of mass 1 kg tied to a light inextensible string of length is whirling in a circular path of radius L in a vertical plane. If the ratio of the maximum tension in the string to the minimum tension in the string is 4 and if g is taken to be 10 m/s2 , the speed of the stone at the highest point of the circle is
Explanation:-
Answer: Option D. -> 10 m/sec:
D
Since the maximum tension TB in the string moving in the vertical circle is at the bottom and minimum tension TT is at the top.
TB = mvB2L = mg and TT = mvT2L - mg
∴ TBTT = mvB2L+mgmvT2L−mg or vB2+gLvT2+gL = 41
or vB2 + gL = 4vT2 - 4gL but vB2 = vT2 + 4gL
∴ vT2 + 4gL +gL ⇒ 3 vT2 = 3gL
∴ vT2 = 3 × g × L = 3 × 10 × 103 or vT = 10 m/sec
Explanation:-
Answer: Option B. -> √3:
B
Let ^n1 and ^n2 are the two unit vectors, then the sum is
⃗ns = ^n1 + ^n2 or ns2 = n12 + n22 + 2n1n2cosθ
= 1 + 1 + 2cosθ
Since it is given that ns is also a unit vector, therefore 1 = 1+ 1 + 2 cos θ = ⇒ cos θ = - 12 ∴ θ = 120∘
Now the difference vector is ^nd = ^n1 - ^n2 or n12 + n22 - 2n1n2cosθ = 1 + 1 - 2 cos(120∘)
∴ nd2 = 2 - 2(- 12) = 2 + 1 = 3 ⇒ nd = √3
Explanation:-
Answer: Option B. -> 150∘:
B
B2 = √A2+B2+2ABcosθ ..(i)
∴ tan 90∘ = BsinθA+Bcosθ ⇒ A + Bcosθ = 0
∴ cos θ = - AB
Hence, from (i) B24 = A2+B2−2A2 ⇒ A = √3B2
⇒ cos θ = - AB = - √32 ∴ θ = 150∘
Explanation:-
Answer: Option D. -> 14.14 ms−1 in south-west direction:
D
If the magnitude of vector remains same, only direction change by θ then
⃗△v = ⃗v2 - ⃗v1, ⃗△v = ⃗v2 + (- ⃗v1)
Magnitude of change in vector |⃗△v| = 2 v sin (θ2)
|⃗△v| = 2 × 10 × sin(90∘2) = 10 √2 = 14.14 m/s
Direction is south - west as shown in figure.
Explanation:-
Answer: Option D. -> 13:
D
Rmax = A + B = 17 when θ = 0∘
Rmin = A - B = 7 when θ = 180∘
by solving we get A = 12 and B = 5
Now when θ = 90∘ then R = √A2+B2
⇒R=√(12)2+(5)2 = √169 = 13
Explanation:-
Answer: Option C. -> 5, 13:
C
Let P be the smaller force and Q be the greater force then according to problem-
P + Q = 18 ..(i)
R = √P2+Q2+2PQcosθ = 12 ..(ii)
tan ϕ = QsinθP+Qcosθ = tan 90 = ∞
∴ P + Q cos θ = 0 ..(iii)
By solving (i), (ii) and (iii) we will get P = 5 , and Q = 13