A stone used in the sport of curling has a mass of 20.0 kg and is initially at rest, sitting on a flat ice surface. It is pushed with a constant force of magnitude 25.0N over a distance of 4.00 m. (Assume friction between the stone and the ice is negligible.)

Question

(a) (i) What is the acceleration of the stone and what is the work done in accelerating it?

(ii) By considering the conservation of energy of the stone, calculate the final speed of the stone. Show that you have checked that the value for the magnitude of speed and its unit are sensible.

(b) How much power is supplied by the person pushing the stone at the beginning of the push and how much is supplied at the end of the push?

(c) Calculate the duration of the push from the acceleration and final speed. Compare this with the time calculated from the average power supplied during the push and the amount of work done.

Answer 1

(a) (i) The acceleration of the stone is 2.5 m/s^2 and the work done in accelerating it is 100 J.

(ii) The final speed of the stone is 10 m/s. The magnitude of the speed is sensible since it is less than the speed of light. The unit of the speed is also sensible since it is in m/s.

(b) The power supplied by the person pushing the stone at the beginning of the push is 625 W and the power supplied at the end of the push is 312.5 W.

(c) The duration of the push from the acceleration and final speed is 4 s. The time calculated from the average power supplied during the push and the amount of work done is also 4 s.