NJC Energy & Fields Problem Set 2025

National Junior College Science Department | Physics 4. Energy & Fields Problem Set 4.1 ENERGY STORES AND TRANSFERS 4.1.1 Exercises For this section of the problem set, you should try the exercises without looking at the solutions. The solutions are there if you get stuck and you should also use it to understand how to present your work. E1 An arrow is placed on the string of a bow and pulled back before being released from the bow. Describe the energy stores and transfers of the arrow. 4.1.2 Problem P1. N12/1/10 The top end of a spring is attached to a fixed point and a mass of 4.2 kg is attached to its lower end. The mass is released and after bouncing up and down several times it comes to rest at a distance 0.29 m below its starting point. Which row gives the gain in the gravitational potential energy of the mass Ep and the gain in the elastic potential energy of the spring Es? Ep / J Es / J A –12 +12 B –12 +6 C +12 +12 D +12 +6 4.2 WORK DONE BY A FORCE 4.2.1 Exercises E2 (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]

National Junior College Science Department | Physics E3 (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. E4 An object at rest is pulled by a constant horizontal force, F on a smooth floor to a displacement of x. (a) Sketch a graph of force applied on object against the displacement. Label F and x in the graph. (b) What does the area under force against displacement graph in (i) represent? E5 An object at rest is pulled by a varying horizontal force, Fx on a smooth floor to a displacement of x. (a) Can we still use this formula to calculate the work done by Fx, i.e workdone = Fx(x)? (b) How can the work done by Fx be calculated? 4.2.2 Problems P2. 2011/P1/Q11 A constant force F is applied to a stationary object of mass m on a frictionless surface. A constant acceleration increases the velocity of the object to some value v in a time t. It covers a distance s during this time. Which value of energy is given to the object’s kinetic store? A Fst B Fv C Fs D 2 ms t P3. A force F that is parallel to the x-axis acts on a block of ice. The magnitude of the force varies with the x-coordinate of the block as shown. Calculate the work done on the block of ice by the force F when the block moves from x = 0 m to x = 7.0 m