# Issues of Friction

I'm completely lost - Could you go step by step so I can follow your logic? Thanks.

1. A crate sits on a flatbed truck. This truck, initially travelling at a velocity of 80 km/hour, comes to a stop in 22 meters. What is the minimum coefficient of static friction required between the crate and truck bed, if it is not to slide forward?

2. A hospital traction device is shown in (attached). What is a) the horizontal force and b) the vertical force exerted on the foot by the arrangement, if the cord transmits an undiminished tension T of 5.0 gN?

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#### Solution Preview

1) Recall that acceleration is the change in velocity over change in time.

Look at the units: v = 80 km/hr = 80,000 m/hr = 22 m/s (initial velocity)

Use the following equation to find the acceleration: v^2 = (vo)^2 + 2a(x-xo), where v^2 is velocity squared, (vo)^2 is initial velocity squared, a is acceleration, x is position, and xo is the ...

#### Solution Summary

The answers are determined by looking at the relationships between velocity and acceleration and frictional force. The minimum coefficient of friction and the horizontal/vertical forces are calculated by using all these parameters and the variable of time.

Basic Physics Problems (Force; Newton's Second Law; Horizontal Force; Net Force; Static Friction; Kinetic Friction)

I would like for you to show me all of your work/calculations and the correct answer to each problem.

15. A 5.0-kg block at rest on a frictionless surface is acted on by forces F1 = 5.5 N and F2 = 3.5 N. What additional horizontal force will keep the block at rest?

19. The engines of most rockets produce a constant thrust (forward force). However, when a rocket is fired into space, its acceleration increase with time as the engine continues to operate. Is this situation a violation of Newton's second law? Explain.

23. What is the mass of an object that accelerates at 3.0 m/s[squared] under the influence of a 5.0-N net force?

29. What is the weight of an 8.0-kg mass in newtons? How about in pounds?

33. A horizontal force of 12 N acts on an object that rests on a level, frictionless surface on the Earth, where the object has a weight of 98 N. (a) What is the magnitude of the acceleration of the object? (b) What would be the acceleration of the same object in a similar situation on the Moon?

35. When a horizontal force of 300 N is applied to a 75.0-kg box, the box slides on a level floor, opposed by a force of kinetic friction of 120 N. What is the magnitude of the acceleration of the box?

39. A jet catapult on an aircraft carrier accelerates a 2000-kg plane uniformly from rest to a launch speed of 320 km/h in 2.0 s. What is the magnitude of the net force of the plane?

49. In an Olympic figure-skating event, a 60-kg male skater pushes a 45-kg female skater, causing her to accelerate at a rate of 2.0 m/s[squared]. At what rate will the male skater accelerate? What is the direction of his acceleration?

53. The weight of a 500-kg object is 4900 N. (a) When the object is on a moving elevator, its measured weight could be (1) zero, (2) between zero and 4900 N, (3) more than 4900 N, or (4) all of the preceding. Why?

(b) Describe the motion if the object's measured weight is only 4000 N in a moving elevator.

59. A girl pushes a 25-kg lawn mower. If F = 30 N and 0 = 37 degrees, (a) what is the acceleration of the mower, and (b) what is the normal force exerted on the mower by the lawn? Ignore friction.

65. A 3000-kg truck tows a 1500-kg car by a chain. If the net forward force on the truck by the ground is 3200 N, (a) what is the acceleration of the car, and (b) what is the tension in the connecting chain?

83. A 40-kg crate is at rest on a level surface. If the coefficient of static friction between the crate and the surface is 0.69, what horizontal force is required to get the crate moving?

87. A hockey player hits a puck with his stick, giving the puck an initial speed of 5.0 m/s. If the puck slows uniformly and comes to rest in a distance of 20 m, what is the coefficient of kinetic friction between the ice and the puck?

93. While being unloaded from a truck, a 10-kg suitcase is placed on a flat ramp inclined at 37 degrees. When released from rest, the suitcase accelerates down the ramp at 0.15 m/s[squared]. What is the coefficient of kinetic friction between the suitcase and the ramp?

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