A car moving with a velocity of 20 ms-1 stopped at a distanc

Subject

Physics

Class

JEE Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

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1.

A car moving with a velocity of 20 ms-1 stopped at a distance of 40 m. If the same car is travelling at double the velocity, the distance travelled by it for same retardation is

  • 320 m

  • 1280 m

  • 160 m

  • 640 m


C.

160 m

Velocity of car (u) = 20 ms-1

Distance (s) = 40 m

From Newton's third equation,

       v2 - u2 = 2as       v2 - u2 = - 2 as02 - 202 = - 2 (a) × 40              400 = 2 × 40 × a                  a = 4002 × 40                  a = 5 ms-2

In the second condition, the velocity becomes twice i.e, u' = 2u

Again from Newton's third equation, we get

02 - 2u2 = 2 × 5 × s                  s = 2u22 × 5                  s = 4u22 × 5                  s = 4 × 20 × 202 × 5                  s = 160 m


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2.

A substance of mass 49.53 g occupies 1.5 cm3 of volume. The density of the substance (in g cm-3) with correct number of significant figures is

  • 3.3

  • 3300

  • 3302

  • 33.0


3.

Two balls are thrown simultaneously in air. The acceleration of the centre of mass of the two balls when in air

  • is equal to g (acceleration due to gravity)

  • depends on the speeds of the two balls

  • depends on the masses of the two balls

  • depends on the direction of motion of the two balls


4.

A body of the mass 50 kg is suspended using a spring balance inside a lift at rest. If the lift starts falling freely, the reading of the spring balance is

  • < 50 kg

  • = 50 kg

  • > 50 kg

  • = 0


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5.

The S.I. unit of specific heat capacity is

  • JK-1

  • J kg-1

  • J mol-1 K-1

  • J kg-1 K-1


6.

The value of acceleration due to gravity at a depth of 1600 km is equal to

  • 4.9 ms-2

  • 9.8 ms-2

  • 7.35 ms-2

  • 19.6 ms-2


7.

A motor pump lifts 6 tonnes of water from a well of depth 25 m to the first floor of height 35 m from the ground floor in 20 minutes. The power of the pump (in kW) is [g = 10 ms-2]

  • 3

  • 12

  • 15

  • 6


8.

If A = 2i^ + 3j^ + 8k^ is perpendicular to B = 4j^ - 4i^ + αk^, then the value of α is

  • - 12

  • 12

  • 1

  • − 1


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9.

The angle between velocity and acceleration of a particle describing uniform circular motion is

  • 180°

  • 90°

  • 45°

  • 60°


10.

For which combination of working temperatures, the efficiency of engine is the least ?

  • 100 K, 80 K

  • 40 K, 20 K

  • 80 K, 60 K

  • 60 K, 40 K


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