PHYS 1P21 Lecture 26: Work and Energy IV

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greenspider989

9 Jun 2016

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Example: a child of mass 40 kg slides along a frictionless slide, starting from rest at point a. Determine the child"s speeds at points b, c, and d. the point b is 15 m below a, c is 5 m below. A, and d is 22 m below a. Solution: a good first step is to choose a coordinate system. I"ll choose up to be the positive direction (the horizontal direction is not very relevant in this problem), and i"ll choose to set y= 0 at the level of point d, as shown in the following diagram: Consider the system to be the child plus the ramp plus the earth. There are no external forces on the system, so the total energy is conserved. Because there is no friction, and no air resistance, the total mechanical energy is conserved. The total kinetic energy at point a is zero, because the child starts from point a at rest.

Related Questions

(b) Is the mass of the child a factor in determining his speed at the bottom of the slide?

(c) The child drops straight down rather than following the curved ramp of the slide. In which case will he be traveling faster at ground level?

(d) If friction is present, how would the conservation-of-energy equation be modified?

(e) Find the maximum speed of the child when the slide is frictionless if the initial height of the slide is 12.0 m.

emeraldgerbil245

A child of mass m starts from rest and slides without friction from a height h along a slide next to a pool (Fig. P8.13). She is launched from a height h/5 into the air over the pool. We wish to find the maximum height she reaches above the water in her projectile motion. (a) Is the child–Earth system isolated or non-isolated? Why? (b) Is there a nonconservative force acting within the system? (c) Define the configuration of the system when the child is at the water level as having zero gravitational potential energy. Express the total energy of the system when the child is at the top of the waterslide. (d) Express the total energy of the system when the child is at the launching point. (e) Express the total energy of the system when the child is at the highest point in her projectile motion. (f) From parts (c) and (d), determine her initial speed v_i at the launch point in terms of g and h. (g) From parts (d), (c), and (f), determine her maximum airborne height y_max in terms of h and the launch angle θ. (h) Would your answers be the same if the waterslide were not frictionless? Explain.

lemonmuskrat466

(a) A child slides down a water slide at an amusement park from aninitial height h. The slide can be considered frictionless becauseof the water flowing down it. Can the equation for conservation ofmechanical energy be used on the child?

1
yes
no

(b) Is the mass of the child a factor in determining his speed atthe bottom of the slide?

2
yes
no

(c) The child drops straight down rather than following the curvedramp of the slide. In which case will he be traveling faster atground level?

3
following the curved ramp
dropping straight down
same speed in either case

(d) If friction is present, how would the conservation-of-energyequation be modified?
4

(e) Find the maximum speed of the child when the slide isfrictionless if the initial height of the slide is 12.0 m.
5 m/s

PHYS 1P21 Lecture 26: Work and Energy IV

PHYS 1P21 Full Course Notes

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Physics: Principles with Applications

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