Physics : Work, Energy and Power

Momentum of a body of mass 1 kg is 10 kg-m/s, then its kinetic energy will be

• 100 J

• 50 J

• 1000 J

• 200 J

If the heat of 110 J is added to a gaseous system, whose internal energy is 40 J. Then the amount of external work done is

• 140 J

• 70 J

• 110 J

• 150 J

A bomb of mass 16 kg at rest explodes into two pieces of masses 4 kg and 12 kg. The  velocity of the 12 kg mass is 4 ms^-1 . The kinetic energy of the other mass is

• 192 J

• 96 J

• 144 J

• 288 J

A particle is acted upon by a conservative force F = $\left(7\stackrel{\wedge }{\mathrm{i}} - 6\stackrel{\wedge }{\mathrm{j}}\right)$ N (no other force is acting on the particle). Under the influence of this force, particle moves from (0,0) to (-3m, 4m), then

• work done by the force is 3 J

• work done by the force is − 45 J

• at (0, 0) speed of the particle must be zero

• at (0, 0) speed of the particle must not be zero

If W₁ , W₂ and W₃ represent the work done in moving a particle from A to B along three different paths 1, 2 and 3 respectively in the gravitational field of a point mass m shown in the figure, find the correct relation between W₁ , W₂ and W₃ .

• W₁ > W₂ > W₃

• W₁ = W₂ = W₃

• W₁ < W₂ < W₃

• W₂ > W₁ > W₃

The potential energy of a certain spring when stretched through a distance x is 20 J. The amoµnt of work that must be done on this spring to stretch it through an additional distance $\frac{\mathrm{x}}{2}$ will be

• 20 J

• 25 J

• 5 J

• 15 J

The driver of a truck travelling with a velocity v suddenly notice a brick wall infront of him at a distance r. How the driver avoid himself by crashing into the wall ?

• By speeding up the truck

• By applying a brake

• By slowing down the truck

• By taking a circular turn

A toy rocket of mass 0.1 kg has a small fuel of mass 0.02 kg, which it burns out in 3s. Starting from rest on a horizontal smooth track, it get a speed of 20 ms^-1 after the fuel is burn out. The energy content per unit mass of the fuel is (Ignore the small mass variation of the rocket during fuel burning)

• 20 J/kg

• 100 J/Kg

• 1000 J/kg

• 400 J/kg

Three points charges q, -2q and -2q are placed at the vertices of an equilateral triangle of side a. The work done by some external force to increase their separation to 2a will be

• $\frac{1}{4{\mathrm{\pi \epsilon }}_0} \frac{2{\mathrm{q}}^2}{\mathrm{a}}$

• $\frac{1}{4{\mathrm{\pi \epsilon }}_0} \frac{{\mathrm{q}}^2}{2\mathrm{a}}$

• $\frac{1}{4{\mathrm{\pi \epsilon }}_0} \frac{8\mathrm{q}}{{\mathrm{a}}^2}$

• 0

A wooden ball of density ρ is immersed in water of density σ to depth h and then released, then the height x above the surface of water upto which the ball jumps out of water is equal to

• $\left(\frac{\mathrm{\rho }}{\mathrm{\sigma }} - 1\right)\mathrm{h}$

• $\left(\frac{\mathrm{\sigma }}{\mathrm{\rho }} - 1\right)\mathrm{h}$

• $\left(1 - \frac{\mathrm{\sigma }}{\mathrm{\rho }}\right)\mathrm{h}$

• $\left(1 - \frac{\mathrm{\rho }}{\mathrm{\sigma }}\right)\mathrm{h}$