III 47% 8:10 PM c) In which direction must that force act? d) What supplies that force to the ball? e) Taking g to be 9.8 N/kg, what size force will the Earth supply to the ball when it is at rest on the floor? 11. A toy car moves around a loop-the-loop track. The loop is 0.5 m high. What is the minimum speed of the car at the top of the loop for it to stay on the track? 12. A boy is swinging a toy on a piece of string in a vertical circle. The toy has a mass of 150 g and the radius of the circle is 0.8 m. a) He swings the toy with a linear velocity of 2 m/s. Will the toy move in a circle? Explain your answer. b) Another boy swings the toy with a linear velocity of 3.5 m/s. Work out the tension in the string at the top of the circle, at the bottom of the circle and halfway between the top and the bottom of the circle. 13. A geostationary satellite for communications seems to be in a fixed spot above the equator because it has the same angular velocity as the earth. a) Show that if it goes round once a day, its angular velocity w is a little over 7 x 10-³ rad/s. b) Geostationary satellites are placed in orbits of radius 4.2 x 10 m. Use this information to deduce g, the acceleration of a freely falling body, at this height. 14. At ground level g is 9.8 m/s². Suppose the Earth started to increase its angular velocity. How long would a day be when people on the equator were just 'thrown off'? Why is the expression 'thrown off' a bad one? 15. Two cars A and B are moving along a straight road in the same direction with velocities of 25 km/h and 30 km/h, respectively. Find the velocity of car B relative to car A. 16. Two aircraft P and Q are flying at the same speed, 300 m s¹¹. The direction along which P is flying is at right angles to the direction along which Q is flying. a) Find the magnitude of the velocity of the aircraft P relative to aircraft Q. b) Find the direction of the velocity. 17. A river flows at 2 m/s. The velocity of a ferry relative to the shore is 4 m/s at right angles to the current. What
is the velocity of the ferry relative to the current?
