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Physics problems: conservation laws

Energy-work theorem

 

Problem 1.

If a 5 tons beam is raised 6 meters, what is it's potential energy? If it is raised another 8 meters in 6 seconds, what is the work done?

Solution

 

Problem 2.

(University Physics, 12th Edition, Young & Freedman 6.33) A 10-kg box moving at 5 m/s on a horizontal, frictionless surface runs into a light spring of force constant 100 N/cm. Use the work-energy theorem to find the maximum compression of the spring.

Solution

 

Problem 3.

A cat stuck up a tree and has 500 J gravitational potential energy. It then falls. Find the kinetic energy of the cat just before it is caught by the owner. Find the kinetic energy of the cat after it is caught by the owner. Find the wasted energy (after cat is caught by the owner).

Solution

 

Problem 6.

A metal surface is illuminated one by one by photons of energy 2 eV and 4 eV respectively. The work function of the metal is 0.5 eV. What is the ratio of the maximum speeds of electrons emitted in two cases?

Solution

 

Problem 13.

A cyclist intends to cycle up a 8 degrees hill whose vertical height is 150 m. If each complete revolution of the pedals moves the bike 6 m   along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 30 cm. The total mass of the cyclist and his bike is 100 kg.

Solution

 

Problem 18.

A bullet travelling horizontally losses 1/20 th of its velocity while penetrating a wooden plank, how many such planks are required to stop the bullet.

Solution

 

Problem 19.

If a body losses half of its velocity on penetrating 3cm in a wooden block then how much will it penetrate more before coming to rest.

Solution

 

Problem 22.

The work done by the heart is 1 joule per beat.  Calculate the power of the heart if it beats 72 times in one minute.

Solution

 

 

 

 

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