Question 1

A car is being towed at constant velocity on a horizontal road using a horizontal chain.The tension in the chain must be equal to the weight of the car in order to maintain constant velocity.

Accepted Answer

The tension in the chain must balance the frictional forces opposing the car's motion, not its weight, to maintain constant velocity. The weight of the car is counteracted by the normal force from the road.

Question 2

Which of the following is an accurate statement?

Accepted Answer

The ratio stress/strain is indeed called the elastic modulus.

B, C, D, and E are inaccurate statements. "Strain" is not close in meaning to "force" (B), "stress" is not close in meaning to "stretch" (C), tensile stress is not measured in Newtons (D), and tensile strain is not measured in meters (E).

Question 3

A box of mass m is pulled with a constant acceleration a along a horizontal frictionless floor by a wire that makes an angle of 15 degrees above the horizontal.The tension in this wire is greater than ma.

Accepted Answer

The tension in the wire is given by T = (m*a)/cosθ, where θ is the angle the wire makes with the horizontal. As θ is greater than 0 degrees, cosθ is less than 1. Therefore, T is greater than ma.

Question 4

A stone rolls down a sloping hillside.The normal force that the surface of the hill exerts on the stone is equal to the stone's weight.

Accepted Answer

The normal force that the surface of the hill exerts on the stone is equal and opposite to the component of the stone's weight perpendicular to the surface of the hill. Therefore, the normal force is less than the weight of the stone.

Question 5

Two unequal weights are connected by a massless string which passes over a frictionless pulley.If the pulley has no appreciable mass,the tension in the string is the same on both sides of the pulley;but if the pulley has mass,the tension will not be the same on both sides of the pulley.

Accepted Answer

This is true as the mass of the pulley will add an additional force which will affect the tension in the string on either side of the pulley, making it unequal.

Question 6

Two blocks,A and B,are being pulled to the right along a horizontal surface by a horizontal 100 N pull,as shown in the figure.Both of them are moving together at a constant velocity of 2.0 m/s to the right,and both weigh the same.Which of the figures below shows a correct free-body diagram of the horizontal forces acting on lower block,B?

Accepted Answer

Block B experiences a normal force from the surface equal in magnitude and opposite in direction to its weight. Block A also experiences the same normal force from the surface. The tension force from the rope is transmitted through both blocks and is therefore the same magnitude for both blocks. Since both blocks are moving together at a constant velocity, the net force on block B must be zero. This means that the tension force from the rope must be equal in magnitude and opposite in direction to the frictional force on block B. Therefore, the correct free-body diagram for block B is shown in choice B, where the tension force from the rope is equal in magnitude and opposite in direction to the frictional force, and the normal force from the surface is equal in magnitude and opposite in direction to the weight of block B.

Question 7

A man pushes against a rigid,immovable wall.Which of the following is the most accurate statement concerning this situation?

Accepted Answer

According to Newton's third law of motion, for every action, there is an equal and opposite reaction. When the man pushes on the wall with a force of 200 N, the wall exerts an equal and opposite force of 200 N on the man. Therefore, option B is the most accurate statement concerning this situation. Option A is incorrect because the man can exert a force greater than his weight on the wall, but the wall will exert an equal and opposite force on him. Option C is incorrect because the wall exerts a force on the man equal in magnitude but opposite in direction to his force. Option D is incorrect because the man can be in equilibrium if the wall exerts an equal and opposite force on him. Option E is incorrect because there is no mention of friction in the problem statement.

Question 8

An object attached to a spring is pulled across a frictionless surface.If the spring constant is 45 N/m and the spring is stretched by 0.88 m when the object is accelerating at 1.4 m/s2,what is the mass of the object?

Accepted Answer

Explanation:The force exerted by the spring is given by F = -kx, where k is the spring constant and x is the displacement from the equilibrium position. The acceleration of the object is given by a = F/m, where m is the mass of the object. Substituting the given values, we get:1.4 m/s^2 = (-45 N/m)(0.88 m)/mSolving for m, we get:m = 28 kg

Question 9

A force of 30 N stretches a spring 0.73 m from equilibrium.What is the value of the spring constant?

Accepted Answer

Hooke's law: F = kxk = F/x = 30 N / 0.73 m = 41 N/m

Question 10

If two forces of equal magnitude act on an object that is hinged at a pivot,the force acting farther from the pivot must produce the greater torque about the pivot.

Accepted Answer

The answer of If two forces of equal magnitude act...

Question 11

Three forces A, B, and C act on a body as shown. A fourth force F is required to keep the body in equilibrium.
-In the figure,the x-component of force F is closest to:

Accepted Answer

The answer of 
Three forces A, B, and C act...

Question 12

Suppose that a heavy person and a light person are balanced on a teeter-totter made of a plank of wood.Each person now moves in toward the fulcrum a distance of 25 cm.What effect will this have on the balance of the teeter-totter?

Accepted Answer

The answer of Suppose that a heavy person and a...

Question 13

Three forces A, B, and C act on a body as shown. A fourth force F is required to keep the body in equilibrium.
-In the figure,the y-component of force F is closest to:

Accepted Answer

The y-component of force F is equal to the sum of the y-components of the two forces acting on the object. The y-component of the force F1 is +24 N, and the y-component of the force F2 is +8 N. Therefore, the y-component of force F is +24 N + +8 N = +32 N.

Question 14

A spring stretches by 21.0 cm when a 135 N object is attached.What is the weight of a fish that would stretch the spring by 44.9 cm?

Accepted Answer

The spring constant (k) can be calculated using Hooke's Law: F = kx. For the 135 N object, k = 135 N / 0.21 m. Using this k, the weight of the fish is found by F = k * 0.449 m, which equals approximately 289 N.

Question 15

If the forces on an object balance,it does not necessarily follow that the torques balance.

Accepted Answer

This is because torque takes into account not only the magnitude of the force, but also its distance from the axis of rotation. Therefore, if the forces are balanced but are acting at different distances from the axis of rotation, the torques may not be balanced.

Question 16

Do all points on a rigid,rotating body have the same angular acceleration? Support your answer.

Accepted Answer

The answer of Do all points on a rigid,rotating body...

Question 17

-In the figure,a block of mass M hangs in equilibrium.The rope that is fastened to the wall is horizontal and has a tension of 38 N.The rope that is fastened to the ceiling has a tension of 59 N and makes an angle Θ with the ceiling.The angle Θ is:

Accepted Answer

The horizontal component of the tension in the ceiling rope must equal the tension in the horizontal rope. Using trigonometry, 59 * cos(Θ) = 38. Solving for Θ gives approximately 50°.

Question 18

The figure shows two forces acting on an object.They have magnitudes F₁ = 9.6 N and F₂ = 3.2 N.What third force will cause the object to be in equilibrium?

Accepted Answer

The answer of The figure shows two forces acting on...

Question 19

-In the figure,a certain type of string will break if the tension in the string exceeds 300 N.A number of 8-kg weights are hung one below the other from a hook in the ceiling using this string.The number of weights that causes the string to break and the string segment that will break are as follows:

Accepted Answer

When the 4th weight is added, the top string segment will break.The tension in the string is equal to the weight of the weights hanging from it. When the 4th weight is added, the tension in the string will be 4 * 8 kg * 9.8 m/s^2 = 313.6 N, which is greater than the breaking strength of the string. Therefore, the top string segment will break.

Quiz 8: Equilibrium and Elasticity