NUMERICALS ON WORK DONE

Q1 find out the work done when a force of 20N displaces a body through 8m in the direction of the applied force

F= 20N s = 8m

W = F * S = 20N* 8m = 160 Joules

Q2 A magnetic crane lifts a mass of 1500kg through a vertical height of 40m. Calculate the work done in operating the crane. g=9.8m/s2

F = m*g = 1500 kg x 9.8 m/s2

= 14700N

W = F x S= 14700N x 40m= 588000J

Q3 5900 J of work is done by a machine to lift a mass of 100kg vertically upward. Calculate the height to which the mass is lifted upward

F = m x g = 100 kg x 9.8m/s2

=980N

W = F xS S =W/F = 5900 J / 980 N = 6.02m

Q4 Ceratin force acting on a 20kg mass changes its velocity from 5m/s to 2 m/s. Calculate the work done by the force

Work done = change in kinetic energy = ½ m( v2 – u2)

= ½ x 20 kg x ( 22 - 52)m2/s2

= 10 x (-21) joules= -210 Joules

TRY YOURSELFQ1 A boy weighs 40 kg climbs up a tree of height 5m . Calculate the amount of work done . take g=9.8 m/s2 ans 1960J

Q2 calculate the work done by a man holding a suitcase weighing 5 kg in his hand Ans W=0

Q3 A force of 500N moves a body through a distance of 100cm. calculate the work done by the force. Ans 500J

Q4 A horizontal force of 50N displaces an object of mass 100 kg . Calculate the distance moved and work done by the force in 8 seconds ans= 16m ; 800J

Q5 A man does a work of 5kJ in lifting a 20kg bucket from the ground floor to the top floor of the building. Calculate the height of the building ans 25.5m

Q6 A car of mass 1500kg traveling at the speed of 30m/s stops after covering a distance of 50m when brakes are applied. Calculate a) the force exerted on it by the brakes b) work done by the brakes

ans F= -13500N; W= 675000J)

Q7 calculate the work done if a force of 1000N causes a displacement of 45m such that the force makes an angle of 600 with the displacement ans 22500J

Q8 A body of mass 500gm slows down from a speed of 5m/s to 3 m/s . find the change in the kinetic energy of the body. Ans - 4 J

Q9 Calculate the work done to stop a car of 1500 Kg by moving at a velocity of 60 km/hAns - 208333.33J

Q10 Derive an expression for the kinetic energy of a body which starts from rest and acquires a velocity under the action of constant force