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In which of the following situations is there zero net force on the body? (i) An airplane flying due north at a steady 120 m/s and at a constant altitude; (ii) a car driving straight up a hill with a 3° slope at a constant 90 km/h; (iii) a hawk circling at a constant 20 km/h at a constant height of 15 m above an open field; (iv) a box with slick, frictionless surfaces in the back of a truck as the truck accelerates forward on a level road at 5 m/s2.
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- One or more external forces are exerted on each object enclosed in a dashed box shown in the figures below. Identify the reaction to each of these forces. (Assume that (a), (b) and (c) occur on Earth while (d), (e) and (f) occur far from any outside gravitational influences. Select all that apply.) m Contact forces www. Field forces M (a) the spring exerts a force to the left on the wall upward on the Earth to the right on the wall downward on the Earth to the right on the hand to the left on the hand X b e +Q C Iron Narrow_forwardContact forces Ww. a Field forces +Q S M Iron N m earrow_forwardCalculate the force required to pull a stuffed toy duck (mass m = 1.75 kg) at a constant velocity of 3.8 m/s horizontally across the floor if the string is 49.0° above the horizontal. The coefficient of kinetic friction between the duck and the floor is 0.60.arrow_forward
- A four-person bobsled (total mass =630 kg) comes down a straightaway at the start of a bobsled run.The straightaway is 80.0 m long and is inclined at a constant angle of 10.2 with the horizontal. Assume that the combined effects of friction and air drag produce on the bobsled a constant force of 62.0 N that acts parallel to the incline and up the incline. Answer the following questions to three significant digits. (a) If the speed of the bobsled at the start of the run is 6.20 m/s, how long does the bobsled take to come down the straightaway? (b) Suppose the crew is able to reduce the effects of friction and air drag to 42.0 N. For the same initial velocity, how long does the bobsled now take to come down the straightaway?arrow_forwardA person drags a sled across a frozen lake to town. The surface of the lake is quite smooth and slippery (so the friction from the ice can be neglected), but he has studded boots with nails driven through the soles (from the inside) so he can walk across the ice without slipping. Once the sled is moving at a reasonable speed (about the pace he can walk comfortably), in order to keep the sled moving at this speed he needs to Pull with a constant force. Not pull at all. Pull with a decreasing force. Pull with an increasing force.arrow_forwardWhich is greater? Which has a greater horizontal component, a 100-N force directed at an angle of 60° above the horizontal or a 60-N force directed at an angle of 30° above the horizontal?arrow_forward
- Suppose a rocket is at an elevation of 100 km and has an initial velocity of 1.00 x 10^4 m/s directed vertically upward. If the rocket engines do not burn and no other force other than earth's gravity acts on the rocket, how far does it go?arrow_forwardA cooler (mass 3 kg) is initially at rest on a horizontal floor. It is then pushed in a straight line for 1.5 m by a small child who exerts a horizontal force with magnitude 37.5 N.arrow_forwardA 600 Kg car is moving on a level road at 30 m/s. (a) How large is the retarding force(assumed constant) is required to stop it in a distance of 70 m? (b) What is the minimum coefficient of friction between the tires and the roadway if this is possible ?arrow_forward
- (a) If the coefficient of kinetic friction between tires and dry pavement is 0.80, what is the shortest distance in which you can stop a car by locking the brakes when the car is traveling at 28.7 m/s (about 65 mi/h)? (b) On wet pavement the coefficient of kinetic friction may be only 0.25. How fast should you drive on wet pavement to be able to stop in the same distance as in part (a)? (Note: Locking the brakes is not the safest way to stop.)arrow_forwardSisyphus was a character in Greek mythology and was doomed in Hades to push a boulder to the top of a steep mountain. When he reached the top, the boulder would roll back down the mountain and he would have to start all over again. The coefficient of static friction between the boulder and the mountainside is 0.200, the mass of the boulder is 136kg (300 lbs), and the slope of the mountain is a constant 30.00. What is the force in pounds that Sisyphus must exert on the boulder to move it up the mountain at a constant velocity?arrow_forwardPlease answer fast- Physics A crate of milk chocolate is being moved up a 63° ramp as shown. The crate has a mass of 10 kg. The crate is being pushed by an applied force F=1320 N which is directed perfectly horizontally. The normal force on the crate is FN=1136 N. The crate is subject to kinetic friction as it moves characterized by coefficient of kinetic friction equal to 0.180. The crate moves a distance 1.9 m along the ramp. For each force listed below determine the work done on the crate during this motion. Be sure to include the appropriate + or -. Part A) applied force Part B) force of gravity Part C) normal force Part D) kinetic friction force Part E)T he net work done on the cratearrow_forward
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