A person of mass 62 kg is inside of a lift of mass 940 kg and presses the button on control panel. The lift starts moving upwards with an acceleration 1.0 m/s2. If g = 10 m/s2 ,the tension in the supporting cable is

  • 9680 N

  • 11000 N

  • 1200 N 

  • 1200 N 


B.

11000 N


Total mass = Mass of lift + Mass of person

= 940 +60 = 1000 kg

T - mg = ma

Hence, T - 1000 x 10 = 1000 x 1
 T = 11000 N
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Force F on a particle moving in a straight line varies with distance d as shown in the figure. The work done on the particle during its displacement of 12 m is

  • 21 J

  • 26 J 

  • 13 J

  • 13 J


C.

13 J

Work done = Area under (F - x) graph

= 2 x (7-3) + 

1305 Views

An explosion breaks a rock into three parts in a horizontal plane. Two of them go off at right angles to each other. The first part of mass 1 kg moves with a speed of 12 m/s and the second part of mass 2 kg moves with second part of mass 2 kg moves with 8 m/s speed. If the third part flies off with 4 m/s speed, then its mass is,

  • 3 kg

  • 5 kg

  • 7 kg

  • 7 kg


B.

5 kg

We have,

p1 + p2 + p3 = 0 [ because p = mv]

Therefore,

1 x 12 i  + 2 x 8 j + p3 = 0



Now. p3 = m3 v3

This implies,


2449 Views

A planet moving along an elliptical orbit is closer to the sun at a distance r1 and farthest away at a distance of r2. if v1 and v2 are the linear velocities at these points respectively, then the ratio v1/v2 is

  • r2/r1

  • (r2/r1)2

  • r1 /r2

  • r1 /r2


A.

r2/r1

From the law of conservation of angular momentum

mr1v1 = mr2v2

r1v1 = r2v2

v1/v2 = r2/r1

961 Views

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Uniform magnetic field acting along AB. If the magnetic force on the arm BC Is F, the force on the arm AC is

  • -F
  • F
  • square root of 2 bold F
  • square root of 2 bold F


A.

-F
FAB = 0

FAB + FBC + FCA = 0

FBC + FCA = 0

FBC + FCA = 0

FCA = - FBC = - F
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