Concept explainers
You have been called as an expert witness for a trial in which a driver has been charged with speeding but is claiming innocence. He claims to have slammed on his brakes to avoid rear-ending another car, but tapped the back of the other car just as he came to rest. You have been hired by the prosecution to prove that the driver was indeed speeding. You have received data as follows from the police: Skid marks left by the driver are 56.0 m long and the roadway is level. Tires matching those on the car of the driver have been dragged over the same roadway to determine that the coefficient of kinetic friction between the tires and the roadway is 0.82 at all points along the skid mark. The speed limit on the road is 35 mi/h. Construct an argument to be used in court to show that the driver was indeed speeding.
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Chapter 5 Solutions
Physics for Scientists and Engineers
- You are pushing a wooden crate against a rubber floor. The two surfaces have a static coefficient of friction of 0.45 and a kinetic coefficient of friction of 0.38. The floor is horizontal, and the crate has a mass of 25.0 kg, and is initially at rest. You are pushing with a horizontal force of 155 N. What is the magnitude of the force of friction in this case? Give your answer in units of N, to three significant figures.arrow_forwardConsider an object on an incline where friction is present. The angle between the incline and the horizontal is θ and the coefficient of kinetic friction is μk. Find an expression for the acceleration of this object. Treat down the incline as the positive direction. Calculate the acceleration, in meters per second squared, of this object if θ = 31° and μk = 0.31. Treat down the incline as the positive direction.arrow_forwardA cord passing over a pulley connects two masses, as shown, where m, 3.60 kg and m,6.40 kg. The system accelerates with a magnitude of 1.10 m/s. The coefficient of kinetic friction between the masses and the incline is the same for both masses. Assume the pulley is frictionless, and the cord is massless. (Due to the nature of this problem, do not use rounded intermediate values in your calculations-including answers submitted in WebAssign.) 35.0 35.0 (a) what is the coefficient of kinetic friction? (No Response (b) what is the tension (in N) in the cord? (No Response Narrow_forward
- Find length and give short correct solution..arrow_forwardConsider another special case in which the inclined plane is vertical ( θ = π / 2 ). In this case, for what value of m1 would the acceleration of the two blocks be equal to zero?arrow_forwardMany physical properties, such as force and mass, cannot be measured directly. Rather, some other physical property is measured and the desired physical property is computed from the results. For example, a bathroom scale does not actually measure mass or "weight," but rather the compression distance of a spring. The numerical values on the scale are calibrated from the compression distance using basic physics principles such as Newton's second law. Coefficients of friction cannot be measured directly. In this problem, we are going to learn how we can indirectly measure the coefficient of kinetic friction between two surfaces by directly measuring the expansion of a spring. Consider a 5.45 kg5.45 kg block that is dragged by a spring on a (relatively) frictionless horizontal surface at constant velocity. Suppose the block reaches a rough patch and the spring stretches by 5.25 cm5.25 cm. Compute the coefficient of kinetic friction ?μ between the block and the rough patch if the spring…arrow_forward
- A block with a mass of m=21 kg rests on a frictionless surface and is subject to two forces acting on it. The first force is directed in the negative x direction with a magnitude of F1. The second has a magnitude of F2 and acts on the body at an angle 0=18 degrees measured from horizontal. Write an expression for the magnitude of the normal force, FN acting on the block, in terms if F2 and the other variables of the problem. Assume that the surface it rests on is rigid. The two forces change such that F1=8.5N and F2=19N. Based on this change, the block may no longer be in static equilibrium. Find the blocks acceleration in the x direction, ax, in meters per second squared.arrow_forwardA rocket of mass 4.98 × 105 kg is in flight near earth's surface. Its thrust is directed at an angle of 54.3° above the horizontal and has a magnitude of 9.68 × 106 N. Find the (a) magnitude and (b) direction of the rocket's acceleration. Give the direction as an angle above the horizontal.arrow_forwardSolve it correctly please. I will rate accordingly with 5 votes.arrow_forward
- A 781 N sprinter can push his feet back against the starting blocks with a force of 1852 N in the horizontal direction. If the force is generated for 0.28 s, determine the horizontal velocity of the runner out of the blocks. Include magnitude and direction when reporting vectors.arrow_forwardA box is at rest on a floor. The box has a mass of 35.0 kg. A force P = 213.0 N is acting to the left at an angle = 31.5° above the horizontal as shown in the figure provided on the right. Between the box and the floor, the coefficient of static friction is Hs = 0.830 and the coefficient of kinetic friction is HK = 0.778. What is the magnitude of the normal force acting on the box? P 0 marrow_forwardA block of mass m = 94 kg slides along a horizontal surface. The coefficient of friction between the block and the surface is μk = 0.29. The block has an initial speed of vo = 25 m/s in the positive x-direction as shown. a)Write an expression for the x-component of the frictional force the block experiences, Ff, in terms of the given variables and variables available in the palette. b)What is the magnitude of the frictional force in N? c)How far will the block travel, in meters, before coming to rest?arrow_forward
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