Question 1

A 3-kg box is being lowered on a string at a constant speed. What is the tension in the string? (Assume $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$29.4\ \mathrm{N}$$

Question 2

A 2.04 kg book rests on a table. What is the magnitude of the normal force $$N$$ acting on the book? (Assume $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$20.0\ \mathrm{N}$$

Question 3

A 5 kg block on a circular tabletop is pulled by two horizontal forces: $$F_1 = 2$$\ \mathrm{N}$$ along the +x$-axis and F_2$ = 5\ \mathrm{N} at$$ $$37^\circ$$ above the $$+x-$$axis. What is the magnitude of the net force $$F_{	ext{net}}$$?

Accepted Answer

$$6.0\ \mathrm{N}$$

Question 4

A loudspeaker is held in place by four vertical cables. The tension in each cable is $$30\ \mathrm{N}. $$What is the mass of the loudspeaker? (Assume $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$3.06\ \mathrm{kg}$$

Question 5

A 4.0-kg box sits on a frictionless inclined plane that makes a $$21^\circ$$ angle with the horizontal. It is held in place by a cord parallel to the plane. What is the tension in the cord? (Assume $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$14\ \mathrm{N}$$

Question 6

A 10-kg box moves on a flat surface at $$2\ \mathrm{m/s}. $$The coefficient of kinetic friction between the box and the surface is $$0.4. $$What is the kinetic friction force acting on the box?

Accepted Answer

$$39.2\ \mathrm{N}$$

Question 7

A 5.1 kg block is at rest on the floor. The coefficients of static and kinetic friction are $$\mu_s = 0.7$$ and $$\mu_k = 0.5. $$What force is needed to get the block moving, and what force is needed to keep it moving at constant speed? (Assume $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$F = 35\ \mathrm{N};\ F = 25\ \mathrm{N}$$

Question 8

A 0.50-kg ball is tied to the end of a 4m light cord that spins the ball around in a horizontal plane at constant speed with the cord making a $$30^\circ$$ angle with the vertical. What is the speed of the ball?

Accepted Answer

$$4.43\ \mathrm{m/s}$$

Question 9

A car of mass $$1800\ \mathrm{kg}$$ passes over a bump in a roadway that follows the arc of a circle of radius $$20\ \mathrm{m}. If $$the car moves at a constant $$9\ \mathrm{m/s}$$, what force does the road exert on the car as it moves over the top of the bump?

Accepted Answer

$$10,350\ \mathrm{N}$$

Question 10

A 3-kg block is at rest on an adjustable ramp. When the ramp is tilted to a $$20^\circ$$ angle, the block slides with a constant velocity. What is the coefficient of kinetic friction between the ramp and the block?

Accepted Answer

$$\mu_k = 0.24$$

Question 11

A 10-kg box rests on a frictionless floor, with a 5-kg box on top of it. The coefficients of friction between the boxes are $$\mu_s = 0.7$$ and $$\mu_k = 0.3. $$What is the maximum acceleration the bottom box can have so that the two boxes move together?

Accepted Answer

$$6.86\ \mathrm{m/s^2$}$$

Question 12

A small 4-kg block is tied to the end of a 3-m string and slides around in a circle on a frictionless table. The string will break if the tension exceeds $$50\ \mathrm{N}. $$What is the maximum speed the block can have without breaking the string?

Accepted Answer

$$8.7\ \mathrm{m/s}$$

Question 13

A truck can go around a flat curve of radius $$150\ \mathrm{m}$$ with a maximum speed of $$32\ \mathrm{m/s}$$ before slipping. What is the maximum speed it can go around a tighter curve of radius $$75\ \mathrm{m}$$?

Accepted Answer

$$22.7\ \mathrm{m/s}$$

Question 14

A 5.1 kg cart is pushed along the floor with an unknown force $$F at$$ $$30^\circ$$ below the horizontal. The normal force measured is $$70\ \mathrm{N}. $$What is the horizontal acceleration of the cart? (Assume $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$7.84\ \mathrm{m/s^2$}$$

Question 15

A 20-kg box moving along the floor has a downward force of $$30\ \mathrm{N}$$ acting on it. How hard must you push the box horizontally to keep it moving at a constant $$2\ \mathrm{m/s} if $$the coefficient of kinetic friction $$\mu_k is$$ $$0.3$$?

Accepted Answer

$$67.8\ \mathrm{N}$$

Question 16

A 5kg block A is placed on a 10kg block B. Block A is tied to a wall, while Block B is pulled with a force of $$45\ \mathrm{N}$$ and moves to the right. The coefficient of kinetic friction between all surfaces is $$\mu_k = 0.2. $$What is the tension on Block A?

Accepted Answer

$$1.8\ \mathrm{N}$$

Question 17

A 15 kg block is initially at rest on a horizontal surface. The coefficient of static friction between the block and the surface is $$\mu_s=0.7. $$How hard must you push down on the block to keep a $$300\ \mathrm{N}$$ horizontal force from moving it?

Accepted Answer

$$282\ \mathrm{N}$$

Question 18

A 2.0-kg block is launched up a $$40^\circ$$ ramp at $$10\ \mathrm{m/s}. If $$the block comes to a stop when it reaches a point $$3\ \mathrm{m}$$ vertically above the bottom of the ramp, what is the coefficient of kinetic friction between the block and the ramp?

Accepted Answer

$$0.59$$

Applying Newton's Laws: Forces, Friction, and Circular Motion

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