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Work, Energy and Power · Question 39

AIPMT 2011 (Prelims)MCQMedium📈 Topic in 38% papers+4−1
1

A body projected vertically from the earth reaches a height equal to earth's radius before returning to the earth. The power exerted by the gravitational force is greatest

  1. at the highest position of the body
  2. at the instant just before the body hits the earth.
  3. it remains constant all through.
  4. at the instant just after the body is projected.

Answer

(2) at the instant just before the body hits the earth.

Solution

Power of the gravitational force: P = F v = Fv

At the highest point, v = 0 P = 0.

Just after projection, v is upward and F is downward ( = 180 ) P = -Fv (negative).

Just before hitting the earth, v and F are both downward ( = 0 ), and v and F (near the surface) are maximum.

P is greatest (maximum positive) just before the body hits the earth.

Answer: (2)

AIPMT 2011 (Prelims)

Keep practising — Work, Energy and Power

2

Force F on a particle moving in a straight line varies with distance d as shown in figure. [figure] The work done on the particle during its displacement of 12 m is

  1. 18 J
  2. 21 J
  3. 26 J
  4. 13 J
AIPMT 2011 (Prelims)
3

A particle of mass M, starting from rest, undergoes uniform acceleration. If the speed acquired in time T is V, the power delivered to the particle is

  1. MV2T
  2. 12 MV2T2
  3. MV2T2
  4. 12 MV2T
AIPMT 2010 (Mains)
4

A ball moving with velocity 2 m/s collides head on with another stationary ball of double the mass. If the coefficient of restitution is 0.5, then their velocities (in m/s) after collision will be

  1. 0, 1
  2. 1, 1
  3. 1, 0.5
  4. 0, 2
AIPMT 2010 (Prelims)
5

An engine pumps water through a hose pipe. Water passes through the pipe and leaves it with a velocity of 2 m/s. The mass per unit length of water in the pipe is 100 kg/m. What is the power of the engine?

  1. 400 W
  2. 200 W
  3. 100 W
  4. 800 W
AIPMT 2010 (Prelims)
6

A block of mass M is attached to the lower end of a vertical spring. The spring is hung from a ceiling and has force constant value k. The mass is released from rest with the spring initially unstretched. The maximum extension produced in the length of the spring will be

  1. 2Mg/k
  2. 4Mg/k
  3. Mg/2k
  4. Mg/k
AIPMT 2009
7

A body of mass 1 kg is thrown upwards with a velocity 20 m s-1. It momentarily comes to rest after attaining a height of 18 m. How much energy is lost due to air friction? ( g = 10 m s-2)

  1. 30 J
  2. 40 J
  3. 10 J
  4. 20 J
AIPMT 2009
8

An engine pumps water continuously through a hose. Water leaves the hose with a velocity v and m is the mass per unit length of the water jet. What is the rate at which kinetic energy is imparted to water?

  1. mv3
  2. 12mv2
  3. 12m2v2
  4. 12mv3
AIPMT 2009
9

Water falls from a height of 60 m at the rate of 15 kg/s to operate a turbine. The losses due to frictional forces are 10% of energy. How much power is generated by the turbine ? (g = 10 m/s2)

  1. 12.3 kW
  2. 7.0 kW
  3. 8.1 kW
  4. 10.2 kW
AIPMT 2008
10

A vertical spring with force constant k is fixed on a table. A ball of mass m at a height h above the free upper end of the spring falls vertically on the spring so that the spring is compressed by a distance d. The net work done in the process is

  1. mg(h + d) - 12kd2
  2. mg(h - d) - 12kd2
  3. mg(h - d) + 12kd2
  4. mg(h + d) + 12kd2
AIPMT 2007
11

300 J of work is done in sliding a 2 kg block up an inclined plane of height 10 m. Work done against friction is (Take g = 10 m/s2)

  1. 1000 J
  2. 200 J
  3. 100 J
  4. zero
AIPMT 2006

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