Work, Energy And Power CBSE Questions & Answers

Find the angle between force \({\bf{F}} = 3{\bf{\hat i}} + 4{\bf{\hat j}} - 5{\bf{\hat k}}\)and displacement \({\bf{d}} = 5{\bf{\hat i}} + 4{\bf{\hat j}} + 3{\bf{\hat k}}\)

Find the projection of F on d, if force \({\bf{F}} = 3{\bf{\hat i}} + 4{\bf{\hat j}} - 5{\bf{\hat k}}\)and displacement \({\bf{d}} = 5{\bf{\hat i}} + + 4{\bf{\hat j}} + 3{\bf{\hat k}}\)

Balram exerts a steady force of magnitude 150 N on the stalled car as shown in the figure above; he pushes it a distance of 20 m. The car also has a flat tyre, so to make the car move straight he pushes at an angle of 30\(^\circ \) to the direction of motion. How much work does he do?

Balram exerts a steady force of magnitude F = 200\({\bf{\hat i}}\)+ 2.0\(\hat j\) on the stalled car as shown in the figure above, he pushes it a distance s = 10\({\bf{\hat i}}\) + 10\(\hat j\) m. How much work does he do?

A railway porter is holding a weight of 100 kgs on his head and is standing still. What is the work done by him?

Balram pushes 500kg weight on a frictionless surface a distance of 10 m. The work done by him is

A weight of 20kg falls from a height of 10 m. The work done by the gravitational force is (Take g = 10 m \({{\rm{s}}^{ - {\rm{2}}}}\))

A rain drop of mass 2.00 g falls from a height 1.00 km. It hits the ground with a speed of 50.0 m/s. What is the work done by the gravitational force? (Take g = 10 m \({{\rm{s}}^{ - {\rm{2}}}}\))

A rain drop of mass 2.00 g falls from a height 1.00 km. It hits the ground with a speed of 50.0 m/s. What is the work done by the resistive forces if any? (Take g = 10 m \({{\rm{s}}^{ - {\rm{2}}}}\))

A 6.0-kg block initially at rest is pulled to the right along a horizontal, frictionless surface by a constant horizontal force of 12 N. Find the speed of the block after it has moved 3.0 m.

A 6.0-kg block initially at rest is pulled to the right along a horizontal, surface having a coefficient of kinetic friction of 0.15, by a constant horizontal force of 12 N. Find the speed of the block after it has moved 3.0 m.

A pump on the ground floor of a building can pump up water to fill a tank of volume 30 \({{\text{m}}^{\text{3}}}\) in 15 min. If the tank is 40 m above the ground, and the efficiency of the pump is 30\(\% \), how much electric power is consumed by the pump?

The bob of a pendulum is released from a horizontal position. If the length of the pendulum is 1.5 m, what is the speed with which the bob arrives at the lowermost point, given that it dissipated 5\(\% \) of its initial energy against air resistance?

Consider a collision between two pool balls. Ball 1 is at rest and ball 2 is moving towards it with a speed of 2 m \({{\rm{s}}^{ - {\rm{1}}}}\). The mass of each ball is 0.3 kg. After the balls collide elastically, ball 2 comes to an immediate stop and ball 1 moves off. What is the final velocity of ball 1?

Consider two 2 marbles. Marble 1 has mass 50 g and marble 2 has mass 100 g. Edward rolls marble 2 along the ground towards marble 1 in the positive x-direction. Marble 1 is initially at rest and marble 2 has a velocity of 3 m \({{\rm{s}}^{ - {\rm{1}}}}\) in the positive x-direction. After they collide elastically, both marbles are moving. What is the final velocity of each marble?