Question

1. As part of a child’s game, a girl swings a ball on the end of a string in a horizontal circle with constant speed, as shown below. The string is 0.25m long and makes an angle of 35o with the vertical during the game.

(a) What is the speed of the ball?

(b) During half a revolution, what is the work done by tension and by gravity on the ball?

2. A boy kicks a 3kg box up the side of a hill, which is essentially a flat surface sloping upward at an angle of 35o above the horizontal. As soon as the box leaves the boy’s foot, it has a velocity of 5m/s up the hill. The coefficients of friction between the box and the hill are μs = μk = 0.4.

(a) Determine the magnitude of the force of friction acting on the box as it slides up the hill.

(b) If the box slides a distance D up the hill, write an expression for the work done by friction before the box turns around at the highest point.

(c) Use your expression for the work done by friction and the work-energy theorem to determine D.

(d) At that point, the box turns around and slides back down to the boy. What is the box’s speed when it reaches the boy?

Answer 1

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