## F.Sc ICS Notes: Physics XI: Chapter 4 Work and Energy Numerical Problems

__A man pushes a lawn mover with a 40N force directed at a angle of 20 degree downward from the horizontal. Find the work done by the man as he cuts a strip of grass 20m long.__

**Numerical Problem 4.1:**__A rain drop m = 3.35 * 10(-5)kg falls vertically at a constant speed under the influence of the forces of gravity ad friction. In falling through 100m, how much work is done by:__

**Numerical Problem 4.2:**(a) Gravity:

(b) Friction:

__Ten bricks each 6cm thick and mass 1.5kg, lie flat on a table. How much work is required to stack them one on the top of another.__

**Numerical Problem 4.3:**__A car of mass 800kg traveling at 54km/h is brought to rest in 60 meters. Find the average retarding force on the car. What has happened to the original K.E?__

**Numerical Problem 4.4:**__A 1000kg automobile at the top of an inclined plane 10m high and 100m long is released and rolls down the hill. What is its speed at the bottom of inclined if the average retarding force due to friction is 480N?__

**Numerical Problem 4.5:**__If 100m(3) of water is pumped from a reservoir into a tank, 10 m higher than the reservoir, in 20 minutes. If density of water is 1000kg/m(3), find__

**Numerical Problem 4.6:**(a) The increase in P.E

(b) The power delivered by pump.

__A force(thrust) of 400N is required to overcome road friction and air resistance in propelling an automobile at 80km/h. What power kW must the engine develop?__

**Numerical Problem 4.7:**__How large a force is required to accelerate an electron (m 9.1 * 10 (-31)kg) from rest to a speed of 92 * 10(7)m/s) through a distance of 5cm.__

**Numerical Problem 4.8:**__A diver weighing 750N dive from a board 10m above the surface of the pool pf water. Use the conservation of mechanical energy to find the speed at a point 5m above the water surface, neglecting air friction.__

**Numerical Problem 4.9:**__A child starts from the rest at the top of a slide of height 4m.__

**Numerical Problem 4.10:**(a) What is the his speed at the bottom if the slide is friction less?

(b) If he reaches the bottom, with a speed of 6 m/s. What percentage of his total energy at the top of the slide is lost as a result of friction?

Two cars are moving to each other from opposite directions with same speed the horn of one is blowing with frequency of 3000Hz and is heard by people in other car with frequency of 3400Hz find speed of cars if speed of sound in air is 340m/s how it can be solved

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