Physics : Work, Energy and Power

Three point charges 1 C, 2C and 3C are placed at the corners of an equilateral triangle of side 1 m. The work done in bringing these charges to the vertices of a smaller similar triangle of side 0.5 m is

• 2.7 × 10¹⁰ J

• 9.9 × 10¹⁰ J

• 10.8 × 10¹⁰ J

• 5.4 × 10¹⁰ J

A body of mass 2 kg makes an elastic collision with another body at rest and continues to move in the original direction with one-fourth its original speed. The mass of the second body which collides with the first body is

• 2 kg

• 1.2 kg

• 3 kg

• 1.5 kg

In the stable equilibrium position, a body has 

• maximum potential energy

• minimum potential energy

• minimum kinetic energy

• neither maximum nor minimum potential energy

A particle of mass m at rest is acted upon by a force P for a time t. Its kinetic energy after an interval t is

• $\frac{{\mathrm{P}}^2{\mathrm{t}}^2}{\mathrm{m}}$

• $\frac{{\mathrm{P}}^2{\mathrm{t}}^2}{2\mathrm{m}}$

• $\frac{{\mathrm{P}}^2{\mathrm{t}}^2}{3\mathrm{m}}$

• $\frac{\mathrm{Pt}}{2\mathrm{m}}$

A car of mass 1000 kg accelerates uniformly from rest to a velocity of 54 km/h in 5 s. The average power of the engine during this period in watts is (neglect friction)

• 2000 W

• 22500 W

• 5000 W

• 2250 W

A quarter horse power motor runs at a speed of 600 rpm. Assuming 40% efficiency the work done by the motor in one rotation will be

• 7.46 J

• 7400 J

• 7.46 erg

• 74.6 J

Two bodies of masses 1 kg and 2 kg have equal momentum. Then, the ratio of their kinetic energies is

• 2 : 1

• 3 : 1

• 1 : 3

• 1 : 1

When a body moves in a circular path, no work is done by the force since

• force and displacement are perpendicular to each other

• the force is always away from the centre

• there is no displacement

• there is no net force

A 5.0 amp current is setup in an external circuit by a 6.0 volt storage battery for 6.0 minutes. The chemical energy of the battery is reduced by

• 1.08 × 10⁴ J

• 108 × 10⁴ J

• 1.8 × 10⁴ J

• 18 × 10⁴ J

The relationship between the force F and position x of a body is as shown in figure. The work done in displacing the body from x = 1 m to x = 5 m will be

• 30 J

• 15 J

• 25 J

• 20 J