Numerical Problems 4.1: A man pushes a lawn mower with a 40 N force directed at a angle of 20° downward from the horizontal. Find the work done by the man as he cuts a strip of grass 20 m long.
(Ans: 7.5 ｘ 10² J)
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Numerical Problems 4.2: A rain drop (m = 3.35 ｘ 10⁻⁵ kg) falls vertically at a constant speed under the influence of the forces of gravity ad friction. In falling through 100 m, how much work is done by: (a) Gravity and (b) Friction: (Ans: (a) 0.0328 J, (b) -0.0328 J )
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Numerical Problems 4.3: Ten bricks each 6 cm thick and mass 1.5 kg, lie flat on a table. How much work is required to stick them one on the top of another. (Ans: 40 J)
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Numerical Problems 4.4: A car of mass 800 kg traveling at 54 km h⁻¹ is brought to rest in 60 meters. Find the average retarding force on the car. What has happened to the original K.E? (Ans: 1500 N)
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Numerical Problems 4.5: A 1000 kg automobile at the top of an inclined plane 10 m high and 100 m 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 480 N? (Ans: 10 m s⁻¹)
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Numerical Problems 4.6: If 100 m³⁻³ of water is pumped from a reservoir into a tank, 10 m higher than the reservoir, in 20 minutes. If density of water is 1000 kg m⁻³, find
(a) The increase in P.E
(b) The power delivered by pump.
(Ans: (a) 9.8 x 10⁶ J, (b) 8.2 kW)
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Numerical Problems 4.7: A force (thrust) of 400 N is required to overcome road friction and air resistance in propelling an automobile at 80 km h⁻¹. What power (kW) must the engine develop? (Ans: 8.9 Kw)
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Numerical Problems 4.8: How large a force is required to accelerate an electron (m = 9.1 ｘ10⁻³¹ kg) from rest to a speed of 92 ｘ10⁷ m s⁻¹ through a distance of 5 cm. (Ans: 3.6 ｘ10⁻¹⁵ N)
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Numerical Problems 4.9: A diver weighing 750 N dive from a board 10 m above the surface of the pool pf water. Use the conservation of mechanical energy to find the speed at a point 5 m above the water surface, neglecting air friction. (Ans: 9.9 m s⁻¹)
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Numerical Problems 4.10: A child starts from the rest at the top of a slide of height 4m.
(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?
(Ans: (a) 8.8 m s⁻¹, (b) 54 %)
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2. Website for School and College Level Mathematics
3. Website for Single National Curriculum Pakistan - All Subjects Notes
© 2022-Onwards by Academic Skills and Knowledge (ASK)
Note: Write me in the comment box below for any query and also Share this information with your class-fellows and friends.
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