NJC 2023 Work, Energy, Power Problem Set

National JC Work, Energy and Power 2023 - 1 - WEP Problem Set Exercises Work done E1. (a) Calculate the work done by Denise to drag her basket of laundry of mass 5.0 kg a distance of 5.0 m along a floor, if the force she exerts is 30.0 N at an angle of 60° with the horizontal. [75 J] (b) Hilda holds a gardening book of weight 10 N at a height of 1.0 m above her patio for 50s. Calculate the work done by Hilda during the 50 s? [0 J] E2. (a) Can work done be positive or negative? State the condition for it. (b) Can work done be zero? State the condition(s) for it. Force-extension, EPE E3. The elastic potential energy stored in the bow just before the release of an arrow is 95 J. When the arrow of mass 170 g is fired, 90% of the elastic potential energy is transferred to the arrow. Show that the speed of the arrow as it leaves the bow is 32 m s-1. E4. An object at rest is pulled by a constant horizontal force, F on a smooth floor to a displacement of x. (i) Sketch a graph of force applied on object against the displacement. Label F and x in the graph. (ii) What does the area under force against displacement graph in (i) represent? Hint: work done. E5. An object at rest is pulled by a varying horizontal force, Fx on a smooth floor to a displacement of x. (i) Can we still use this formula to calculate the work done by Fx, i.e workdone = Fx(x)? (ii) How can the work done by Fx be calculated? Kinetic energy E6. Sam pushes a 10 kg sack of rice on a frictionless surface with a constant horizontal force of 2.0 N starting from rest. (a) What is the kinetic energy of the sack after Sam has pushed it a distance of 35 cm? (b) What is the speed of the sack after Sam has pushed it a distance of 35 cm? [0.70 J; 0.37 m s-1] Conservation of Energy E7. A roller coaster is shown in figure below. Assuming no friction, and that the coaster has a speed of 2.80 m s-1 at point A, calculate (a) the speed at point B, and [24.4 m s-1] (b) the speed at point C. [10.3 m s-1]

National JC Work, Energy and Power 2023 - 2 - E8. A block of mass 2.0 kg placed on a smooth table is pressed against a spring as shown below. The spring is compressed by a distance of 10.0 cm from its unstretched length. The block is released and it accelerates until it leaves the spring at O. The spring has a spring constant of 500 N m-1. Calculate (a) the work done in compressing the spring. [2.5 J] (b) the speed of the block when it leaves O. [1.6 m s-1] Power E9. 2009/P1/Q12 A speed boat with two engines, each