## Numerical Problems, Work and Energy

This page consists of solved numerical problems on Work and Energy included in the Physics course for Grade 11.

S.NoDescription of numerical problem
Problem 1A 70 kg man runs up a long flight of stairs in 4 s. The vertical height of the stairs is 4.5 m. Calculate his power.
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Problem 2A body of mass 2.0 kg is dropped from a rest position 5 m above the ground. What is its velocity at height of 3.0 m above the ground?
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Problem 3A man pulls a trolley through a distance of 50 m by applying a force of 100 N which makes an angle of 300 with horizontal. Calculate the work done by the man.
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Problem 4The roller-coaster car starts its journey from a vertical height of 40 m on the first hill and reaches a vertical height of only 25 m on the second hill, where it slows to a momentary stop. It travelled a total distance of 400 m. Determine the thermal energy produced and estimate the average friction force on car whose mass is 1000 kg.
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Problem 5A man whose mass is 70 kg walks up to the third floor of a building which is 12 m above the ground in 20 s. Find his power in watt and horsepower.
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Problem 6To what height can a 400 w engine lift a 100 kg mass in 3 s?
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Problem 7A ball of mass 100 grams is thrown vertically upward at a speed of 25 ms-1. If no energy is lost, determine the height it would reach. If the ball only rises to 25 m, calculate the work done against the air resistance. Also calculate the force of friction.
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Problem 8An object of mass 1000 g falls from a height of 30 m on the sand below. If it penetrates 4 cm into the sand, what opposing force is exerted on it by the sand? Neglect air friction.
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Problem 9

A body of mass m drops from bridge into water of the river. The bridge is 10 m high from the water surface.
(a) Find the speed of the body 5 m above the water surface.
(b) Find the speed of the body before it strikes the water.

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Problem 10The engine of a JF-Thunder fighter develops a thurst of 3000 N. What horsepower does it at a velocity of 600 m/s.
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Problem 11The mass of moon is 1/80 of the mass of the earth and the corresponding radius is 1/4 of the earth. Calculate the escape velocity on the surface of the moon.
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