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SPH3U: Forces Name: _____________________________ Newton’s Laws of Motion 1. Draw the free body diagram in the following cases using the forces indicated. a) a sailboat is experiencing a force of thrust (an applied force) forward due to the wind, the force of gravity downward, a buoyancy force upwards (provided by the water – type of normal force), and a force of water resistance (type of friction) backwards. b) a rocket flying upwards is experiencing a force of thrust upwards, the force of gravity downwards, the force of air resistance (in the opposite direction of the motion), and a force to the right due to a crosswind. 2. In each of the following cases, identify whether the forces acting on the object will be balanced or unbalanced and also state whether the net force is zero or non-zero. a) a puck bounces off a goalie’s pads b) a volcano shoots lava straight up at a constant speed c) a yoyo drops straight down without speeding up d) a car drives along a winding mountain road at a constant speed e) a car comes to a stop while traveling on a straight road f) a jellyfish pushes water backwards so that it can begin to move forward 3. Use Newton’s first law to explain a) why people might fall backwards when a bus starts moving b) why seatbelts in a car are a good idea 4. Find the NET force in each of the following situations. a) a hot air balloon experiences a gravitational force of 5000 N[down] and a lifting force (buoyancy) of 6000 N[up] . b) a submarine experiences the following forces; a force of gravity of 2.5 107 N, a buoyancy force of 2.5 107 N [up], a thrust force of 300,000 N[forward], and a force of water resistance of 300,000 N[backward] c) a jet taking off from a runway experiences a thrust force from the engines of 75,000 N [forwards], and a force of air resistance of 55,000 N 5. In which of the situations in question 4 will the object be accelerating? 6. If a 200 g baseball is accelerating at 7.5 m/s2 [East] what is the net force acting on it? (1.5 N[E] ) 1 7. If an electron (mass 9.10 1031 kg) experiences a force of 5.00 1027 N[forwards] in a TV tube, what will its acceleration be? (5490 m/s2[f] ) 8. If a push of 25 N [left] produces an acceleration of 5.0 m/s2 [left], what is the mass of the object? (5.0 kg) 9. If a 200 kg rocket sled experiences a forward thrust of 25 000 N and an air resistance force of 10 000 N, what will its acceleration be? (Assume the force of gravity and the normal force will cancel each other.) (75 m/s2[f]) 10. A piano mover is pushing a 300 kg piano across a floor. If the piano is accelerating at a rate of 0.10 m/s 2 [forward] and experiencing a frictional force of 140 N[back], what force is the piano mover exerting? (170 N[f] ) 11. A 1600 kg car is being pushed and pulled along a road. If the person pushing is exerting a force of 1200 N[forward], the person pulling is exerting a force of 700 N[forward], and the car is experiencing a force of friction of 2300 N backwards, what is the acceleration of the car? Is it speeding up or slowing down? (0.25 m/s2[f] ) 12. A 285 kg rowboat is being pushed by a forward force of 112 N from the paddles. If it is accelerating at 0.120 m/s2, how much water resistance is it experiencing? (assume gravity and buoyancy cancel each other) (77.8 N[b] ) THE FOLLOWING QUESTIONS REQUIRE YOU TO KNOW NEWTON’S THIRD LAW 13. In the following situations, what are the relevant action-reaction pairs of forces? a) b) c) d) e) f) a stunt-person is fired forwards from a cannon the earth's pulls on an apple attached to a tree a paddle makes a boat go forward a propeller makes an airplane move forward the sailboat described in question 1a) the hot-air balloon described in question 4a) 14. An astronaut (mass 70 kg) is repairing a satellite (mass 700 kg) and is attached to the satellite by a wire. If the astronaut pulls on the wire with a force of 45 N, a) what acceleration will the astronaut have? (0.64 m/s2 [toward sat.] ) b) What will the force on the satellite be? (45 N [toward astro.] ) c) what acceleration will the satellite have? (0.064 m/s2 [toward astro.] ) d) If the pull lasts for 1.5 seconds, and both objects start at rest, what will their speeds be after the astronaut finishes pulling? (0.96 m/s and 0.096 m/s) 2