If a compressive force on the tibia bone in the lower part of an adult person leg exceeds about 4 x 10N, it would break (we assume that the ankle is pushing up). Let's consider that this person steps off a chair that is 0.40 m above the floor. Part A What minimum stopping distance does the person need to avoid breaking his tibias, if landing stiff-legged on the surface below? Suppose that the mass of the human is 65 kg Express your answer to two significant figures and include the appropriate units. HA d = Value Units

If a compressive force on the tibia bone in the lower part of an adult person leg exceeds about 4 x 10N, it would break (we assume that the ankle is pushing up). Let's consider that this person steps off a chair that is 0.40 m above the floor. Part A What minimum stopping distance does the person need to avoid breaking his tibias, if landing stiff-legged on the surface below? Suppose that the mass of the human is 65 kg Express your answer to two significant figures and include the appropriate units. HA d = Value Units

College Physics

10th Edition

ISBN:9781285737027

Author:Raymond A. Serway, Chris Vuille

Publisher:Raymond A. Serway, Chris Vuille

Chapter5: Energy

Section: Chapter Questions

Problem 12CQ: In most situations we have encountered in this chapter, frictional forces tend to reduce the kinetic...

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(a) Calculate the force needed to bring a 950-kg car to rest from a speed of 90.0 km/h in a distance of 120 m (a fairly typical distance for a non-panic stop). (b) Suppose instead the car hits a concrete abutment at full speed and is brought to a stop in 2.00 m. Calculate the force exerted on the car and compare it with the force found in part (a).
At the bottom of an air track tilted at angle , a glider of mass m is given a push to make it coast a distance d up the slope as it slows clown and stops. Then the glider comes back down the track to its starting point. Now the experiment is repeated with the same original speed but with a second identical glider set on top of the first. The airflow from the track is strong enough to support the stacked pair of gliders so that the combination moves over the track with negligible friction. Static friction holds the second glider stationary relative to the first glider throughout the motion. The coefficient of static friction between the two gliders is ,. What is the change in mechanical energy of the two-gliderEarth system in the up- and down-slope motion after the pair of gliders is released? Choose one. (a) 2,mg (b) 2mgd cos (c) 2,mgdcos (d) 0 (e) +2.,mgd cos
In most situations we have encountered in this chapter, frictional forces tend to reduce the kinetic energy of an object. However, frictional forces can sometimes increase an objects kinetic energy. Describe a few situations in which friction causes an increase in kinetic energy.
A child of mass m starts from rest and slides without friction from a height h along a curved waterslide (Fig. P5.46). She is launched from a height h/5 into the pool. (a) Is mechanical energy conserved? Why? (b) Give the gravitational potential energy associated with the child and her kinetic energy in terms of mgh at the following positions: the top of the waterslide, the launching point, and the point where she lands in the pool. (c) Determine her initial speed V0 at the launch point in terms of g and h. (d) Determine her maximum airborne height ymax in terms of h, g, and the horizontal speed at that height, v0x. (e) Use the x-component of the answer to part (c) to eliminate from the answer to part (d), giving the height ymax in terms of g, h, and the launch angle . (f) Would your answers be the same if the waterslide were not frictionless? Explain. Figure P5.46
A child of mass m starts from rest and slides without friction from a height h along a curved waterslide (Fig. P5.46). She is launched from a height h/5 into the pool. (a) Is mechanical energy conserved? Why? (b) Give the gravitational potential energy associated with the child and her kinetic energy in terms of mgh at the following positions: the top of the waterslide, the launching point, and the point where she lands in the pool. (c) Determine her initial speed V0 at the launch point in terms of g and h. (d) Determine her maximum airborne height ymax in terms of h, g, and the horizontal speed at that height, v0x. (e) Use the x-component of the answer to part (c) to eliminate from the answer to part (d), giving the height ymax in terms of g, h, and the launch angle . (f) Would your answers be the same if the waterslide were not frictionless? Explain. Figure P5.46
To get in shape, you head to the local gym to exercise by lifting weights. Using a lat machine (Fig. P5.48), you notice that the wire connected to the bar is run around three different pulleys and is connected to a vertical stack of weights on the other end. The weights move up and down as you pull down on the bar. Suppose you set the machine so that the weight to be lifted is 120.0 lb. When you pull down on the bar, exerting a constant force, the acceleration experienced by the weights is 0.250 m/s2. What tension must exist in the wire connecting the bar and weights under these conditions? Assume the pulleys are massless and frictionless. FIGURE P5.48
Review. The mass of a car is 1 500 kg. The shape of the cars body is such that its aerodynamic drag coefficient is D = 0.330 and its frontal area is 2.50 m2. Assuming the drag force is proportional to 2 and ignoring other sources of friction, calculate the power required to maintain a speed of 100 km/h as the car climbs a long hill sloping at 3.20.
You are driving your car on a straight road with a coefficient of friction between the tires and the road of 0.55. A large piece of debris falls in front of your view and you immediate slam on the brakes, leaving a skid mark of 30.5 m (100-feet) long before coming to a stop. A policeman sees your car stopped on the road, looks at the skid mark, and gives you a ticket for traveling over the 13.4 m/s (30 mph) speed limit. Should you fight the speeding ticket in court?
The system shown in Figure P5.49 has an acceleration of magnitude 1.50 m/s2. Assume that the coefficient of kinetic friction between block and incline is the same for both inclines. Find (a) the coefficient of kinetic friction and (b) the tension in the string.
A 480 g peregrine falcon reaches a speed of 75 m/s in a vertical dive called a stoop. If we assume that the falcon speeds up under the influence of gravity only, what is the minimum height of the dive needed to achieve this speed?
Suppose you use an ideal pulley of the type shown in Figure 5.18(a) to support a car engine of mass 100 kg. Figure 5.18 (a) What would the tension in the rope be?N(b) What force must the ceiling supply, assuming you pull straight down on the rope? Neglect the pulley system's mass.N (upward)
Suppose you use an ideal pulley of the type shown in Figure 5.18(a) to support a car engine of mass 140 kg. Figure 5.18 (a) What would the tension in the rope be? N(b) What force must the ceiling supply, assuming you pull straight down on the rope? Neglect the pulley system's mass. N (upward)