6. Intro to Forces (Dynamics)

Equilibrium in 2D

Multiple Choice
A chandelier is supported from the ceiling by 2 chains. Both chains make a 30° angle with the vertical. The tension in each chain is the same because of symmetry:T₁=T₂=50 N. What is the mass of the chandelier?
Multiple Choice
A sphere hangs suspended by a light string, resting against a vertical wall. The sphere has a mass of 2 kg and the string makes an 80° angle with the horizontal. What is the force from the wall against the ball?
Open Question
Find the tension in each cord in Fig. E5.7 if the weight of the suspended object is w.
Open Question
A large wrecking ball is held in place by two light steel cables (Fig. E5.6). If the mass m of the wrecking ball is 3620 kg, what are (a) the tension TB in the cable that makes an angle of 40° with the vertical and (b) the tension TA in the horizontal cable?
Open Question
A 1130-kg car is held in place by a light cable on a very smooth (frictionless) ramp (Fig. E5.8). The cable makes an angle of 31.0° above the surface of the ramp, and the ramp itself rises at 25.0° above the horizontal. (b) Find the tension in the cable.
Open Question
A picture frame hung against a wall is suspended by two wires attached to its upper corners. If the two wires make the same angle with the vertical, what must this angle be if the tension in each wire is equal to 0.75 of the weight of the frame? (Ignore any friction between the wall and the picture frame.)
Open Question
A football coach sits on a sled while two of his players build their strength by dragging the sled across the field with ropes. The friction force on the sled is 1000 N, the players have equal pulls, and the angle between the two ropes is 20 degrees. How hard must each player pull to drag the coach at a steady 2.0\m/s?
Open Question
In an electricity experiment, a 1.0 g plastic ball is suspended on a 60-cm-long string and given an electric charge. A charged rod brought near the ball exerts a horizontal electrical force F(electric) on it, causing the ball to swing out to a 20 degree angle and remain there. (a) What is the magnitude of F(electric)?
Open Question
An accident victim with a broken leg is being placed in traction. The patient wears a special boot with a pulley attached to the sole. The foot and boot together have a mass of 4.0 kg, and the doctor has decided to hang a 6.0 kg mass from the rope. The boot is held suspended by the ropes, as shown in FIGURE P6.40, and does not touch the bed.a. Determine the amount of tension in the rope by using Newton's laws to analyze the hanging mass.Hint: If the pulleys are frictionless, which we will assume, the tension in the rope is constant from one end to the other.
Open Question
The three ropes in FIGURE EX6.1 are tied to a small, very light ring. Two of these ropes are anchored to walls at right angles with the tensions shown in the figure. What are the magnitude and direction of the tension T3 in the third rope?
Open Question
A mobile at the art museum has a 2.0 kg steel cat and a 4.0 kg steel dog suspended from a lightweight cable, as shown in FIGURE EX7.21. It is found that $theta sub 1$ = 20 degrees when the center rope is adjusted to be perfectly horizontal. What are the tension and the angle of rope 3?
Open Question
A home mechanic wants to raise the 310-kg engine out of a car. The plan is to stretch a rope vertically from the engine to a branch of a tree 6.0 m above, and back to the bumper (Fig. 12–96). When the mechanic climbs up a stepladder and pulls horizontally on the rope at its midpoint, the engine rises out of the car.
(a) How much force must the mechanic exert to hold the engine 0.50 m above its normal position?
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Open Question
(II) The two trees in Fig. 12–54 are 6.2 m apart. A backpacker is trying to lift his pack out of the reach of bears. Calculate the magnitude of the force F→ that he must exert downward to hold a 19-kg backpack so that the rope sags at its midpoint by
(a) 1.5 m.
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Open Question
(I) Three forces are applied to a tree sapling, as shown in Fig. 12–49, to stabilize it. If F→_A = 385 N and F→_B = 515 N , find F→_C in magnitude and direction.
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Open Question
(II) The two trees in Fig. 12–54 are 6.2 m apart. A backpacker is trying to lift his pack out of the reach of bears. Calculate the magnitude of the force F→ that he must exert downward to hold a 19-kg backpack so that the rope sags at its midpoint by
(b) 0.15 m.
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