Lakshya Education MCQs

Question: F=3^i+6^j8^k


If W =F.s find W. 
A.8 N. m
B.20 N. m
C.5 N. m
D.None of these
Answer: Option A
: A

F=3^i+6^j8^k s=2^i+5^j+2^k W =F.s = (3^i+6^j8^k).(2^i+5^j+2^k) = (-6) + (30) + (-16) (^i.^i=1&^i.^j=0) W = 8 N.m

Submit Answer & Explaination

Earn Reward Points by submitting Detailed Explaination for this Question

More Questions on This Topic :

Question 1. Given F=(xy2)^i+(x2y)^jN. The work done by F when a particle is taken along the semicircular path OAB where the coordinates of B are (4,0) is

  1.    653J
  2.    752J
  3.    734J
  4.    Zero
Answer: Option D
: D

GivenF=(xy2)^i+(x2y)^j W = Fxdx+Fydy = xy2dx+x2ydy = 12d(x2y2)=[x2y22](4,0)(0,0)=0
Question 2. A 50 g bullet moving with velocity 10 m/s strikes a block of mass 950 g at rest and gets embedded in it. The loss in kinetic energy will be
  1.    100%
  2.    95%
  3.    5%
  4.    50%
Answer: Option B
: B

Initial K.E. of system = K.E. of the bullet = 12msv2s By the law of conservation of linear momentum msvs+0=msys×vsys vsys=msvsmsys=50×1050+950=0.5m/s Fractional loss in K.E. = 12msv2s12msysv2sys12msv2s By substituting ms=50×103kg,vs=10m/s msys=1kg,vsys=0.5m/s we get Fractional loss = 95100 Percentage loss = 95 %
Question 3. A small block of mass 2 kg is kept on a rough inclined surface of inclination θ=30 fixed in a lift. The lift goes up with a uniform speed of 1 ms1 and the block does not slide relative to the inclined surface. The work done by the force of friction on the block in a time interval of 2 s is.
  1.    Zero
  2.    9.8 J
  3.    29.4 J
  4.    16.9 J
Answer: Option B
: B

Since the lift's speed is constant, in the absence of acceleration, there will be no pseudo-force (referring to the lift as the frame of reference) or additional reaction/thrust due to inclined plane (referring to ground as the reference frame) on the particle.
Therefore, friction =mg sinθacting along the plane.
Distance moved by the particle (or lift) in time t=vt Work done in time t=(mg sinθ)vt(cos(90-θ))=mgsin2θvt
Substituting the Values we get Work = 9.8 J
Question 4. A light and a heavy body have equal kinetic energy. Which one has a greater momentum ?

  1.    The light body
  2.    The heavy body
  3.    Both have equal momentum
  4.    It is not possible to say anything without additional information
Answer: Option B
: B

P=2mEifEareequalthenPm i.e. heavier body will possess greater momentum.

Check all Questions in this Topic : Click HERE