Practice 1. A 12 kg box sits on top of a 38 kg box. C (a) Draw an FBD for each box. (b) Calculate the normal force acting on the 12 kg box. [ans: 120 N [up]] (c) Calculate the normal force acting on the 38 kg box due to the floor. [ans: 490 N [up]] 2. A child has a mass of 36 kg and is sitting on a seat on an amusement park ride. The ride makes the seat move up and down. Determine the normal force acting on the child when the child is (a) moving up at a constant velocity of 12 m/s [ans: 350 N [up]] (b) moving down at a constant velocity of 14 m/s [ans: 350 N [up]] (c) accelerating down at 1.8 m/s [ans: 290 N [up]] 3. A 72 kg person jumps up off a bathroom scale. Determine the acceleration of the person when the scale reads 840 N. [ans: 1.9 m/s [up]] 4. An electrician holds a 3.2 kg chandelier against a ceiling with a force of 53 N [up]. What is the normal force exerted by the ceiling on the chandelier? [ans: 22 N [down]] 4.1 Questions 1. Use Newton's second law and the force of gravity to explain why all objects fall with the same acceleration in the absence of air resistance. K/U 2. Explain why a person with an open parachute has a lower terminal speed than a person with a closed parachute. K/U 3. Why do light objects with large cross-sectional areas fall more slowly in air than heavy objects with small cross- sectional areas? K/U 4. In an action movie, a plane releases a heavy box while in flight. The box is attached to a parachute that opens as soon as it leaves the plane. Part of the way down to the ground, the parachute malfunctions and the box breaks free. Describe the forces acting on the box while it is falling and use them to describe the velocity and acceleration of the box. Use FBDs to explain your reasoning. KUC 5. An astronaut with a mass of 74 kg goes up to the ISS on a mission. During his stay, the gravitational field strength on the station is 8.6 N/kg. T (a) What is the mass of the astronaut on the station? (b) What is the difference between the astronaut's weight on Earth's surface and his weight on the station? (c) Why does the weight of the astronaut change but not his mass when moving from the surface of Earth to the station? (d) Why does the astronaut appear weightless on the station? 6. Copy and complete Table 1 by calculating the weight of an object of mass 20.000 kg at different latitudes on Earth. Use the results to answer the following questions. (a) What is the difference in the weight of the object from the equator to the North Pole? (b) Why does the weight change at different latitudes? (c) Explain why the gravitational field strength increases with latitude. 7. A cargo box on a rocket has a mass of 32.00 kg. The rocket will travel from Earth to the Moon. K/U TA (a) What will happen to the mass of the cargo box during the mission? Explain your reasoning. (b) Determine the weight of the box at the surface of Earth. (c) The weight of the box on the Moon is 52.06 N. Determine the gravitational field strength on the surface of the Moon. 8. Summarize the differences between mass and weight by copying and completing Table 2. K/U Table 2 Variation SI Quantity Definition Symbol unit Method of measuring with location mass weight 9. Copy Table 3 and complete it for a 57 kg object on each planet. T Table 3 Planet Weight (N) g (N/kg) Mercury 188 Table 1 Venus 462 Weight of object Distance from Latitude () (N) g (N/kg [down]) Jupiter 26 Earth's centre (km) 0 (equator) 9.7805 6378 60 360 30 9.7934 6373 9.8192 6362 90 (North Pole) 9.8322 6357 10. A 24 kg object sits on top of a scale calibrated in newtons. Determine the reading on the scale if (a) the object is at rest and no one is pushing on it (b) the object is at rest and someone is pushing on it with a force of 52 N [down] (c) the object is at rest and someone is pulling on it with a force of 74 N [up] TA