Physics : Work, Energy and Power

A ball is dropped to the ground from a height of 2 m. The coefficient of restitution is 0.6. To what height will the ball rebound ?

• 0.41 m

• 0.9 m

• 0.72 m

• 0.28 m

A lift of mass 1000 kg is descending with a speed of 6 ms^-1 . Suddenly the cable of the lift begins to slip and it falls with a constant acceleration a = $\frac{9}{6}$m / s² . What is the kinetic energy of the lift after falling a distance 15 m ?

• 121.3 kJ

• 155.6 kJ

• 147.4 kJ

• 134.1 kJ

Two spherical bodies of mass M and 5 M and radii R and 2R respectively are released in free space with initial separation between their centres equal to 12 R. If they attract each other due to gravitational force only, then the distance covered by the smaller bodyjust before collision, is

• 1.5 R

• 2.5 R

• 4.5 R

• 7.5  R

If mass-energy equivalence is taken into account, when water is cooled to form ice, the mass of water should

• increase

• remain unchanged

• decrease

• first increase then decrease

The kinetic energy of an electron, which is accelerated in the potential difference of l00 V, is

• 1.6 × 10^-17 J

• 1.6 × 10^-14 J

• 1.6 × 10^-10 J

• 1.6 × 10^-8 J

When a force is applied on a moving body, its motion is retarded. Then the work done is

• positive

• negative

• zero

• positive and negative

A particle is displaced from a position $\left(2\stackrel{\wedge }{\mathrm{i}} - \stackrel{\wedge }{\mathrm{j}} + \stackrel{\wedge }{\mathrm{k}}\right)$ to another position $\left(3\stackrel{\wedge }{\mathrm{i}} + 2\stackrel{\wedge }{\mathrm{j}} - 2\stackrel{\wedge }{\mathrm{k}}\right)$ under the action of the force of $\left(2\stackrel{\wedge }{\mathrm{i}} + \stackrel{\wedge }{\mathrm{j}} - \stackrel{\wedge }{\mathrm{k}}\right)$. The work done by the force in an arbitrary unit is

• 8

• 10

• 12

• 16

In elastic collision

• both momentum and kinetic energies are conserved

• both momentum and kinetic energies are not conserved

• only energy is conserved

• only mechanical energy is conserved

A body rolls down an inclined plane. If its kinetic energy of rotation is 40% of its kinetic energy of translation, then the body is

• solid cylinder

• solid sphere

• disc

• ring

Force required to move a mass of 1 kg at rest on a horizontal rough plane (µ = 0.1 and g =9.8 ms^-2) is 

• 0.98 N

• 0.49 N

• 9.8 N

• 4.9 N