physics

posted by .

A 20 kg child on roller skates, initially at rest, rolls 4 m down an incline at an angle of 30 degrees with the horizontal. If there is no friction between incline and skates, what is the kenetic energy of the child at the bottom of the incline? (g= 9.81 m/s^2)

  • physics -

    There are two ways of doing this problem, the energy way and the work way.
    The energy way is to say the potential energy lost by moving down is the kinetic energy gained at the bottom.
    Potential energy lost = m g times the change in height
    The change in height is from:
    sin (30) = change in height / 4
    so change in height = 4 sin 30 = 2 meters down
    so the potential energy lost is:
    m * 9.8 * 2 which is 19.6 m Joules
    That 19.6 m Joules is the kinetic energy at the bottom
    KE = 19.6 m
    since m = 20 kg
    KE = 20*19.6 = 392 Joules
    NOW the other way
    The work done is the force down the ramp times the distance run
    The component of force down the ramp is
    m g cos 60 = 20 *9.8 * .5 = 98 Newtons
    That 98 newtons pushes a distance of 4 meters so the work done is
    98 * 4 = 392 Joules
    That work done is used to increase the kinetic energy of the child so the kinetic energy is also 392 Joules.

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. physics

    need help with this question please a 1kg block starts at rest and slides down the incline. the coefficient of friction between the incline and the block is 0.1. The height of the incline is 2m, and the angle is 30 degrees. use energy …
  2. physics

    A 25 kg box slides, from rest, down a 9-m-long incline making an angle 15 degrees with the horizontal. The speed of the box when it reaches the bottom of the incline is 2.40 m/s. (a) What is the coefficient of kinetic friction between …
  3. Physics

    A 16kg child on roller skates rolls 2m down an incline at 20 degrees with the horizontal. With no friction, what is the total kinetic energy of the child at the bottom of the incline?
  4. Physics

    A 37 kg child roller skates, initially at rest, rolls 2.0 m down an incline at an angle of 17 degrees with the horizontal. If there's no friction, what is the kinetic energy of the child at the bottom of the incline?
  5. Physics

    A 37 kg child roller skates, initially at rest, rolls 2.0 m down an incline at an angle of 17 degrees with the horizontal. If there's no friction, what is the kinetic energy of the child at the bottom of the incline?
  6. Physics

    A 37 kg child roller skates, initially at rest, rolls 2.0 m down an incline at an angle of 17 degrees with the horizontal. If there's no friction, what is the kinetic energy of the child at the bottom of the incline?
  7. Physics Energy and Work

    A 20.0 kg child on skis, initially at rest, slides 2.0 m down an incline at an angle of 20.0 degrees with the horizontal. If there is no friction between incline and skis, what is the kinetic energy of the child at the bottom of the …
  8. Science

    A person roller skates down a street heading West. What is true about friction in this case?
  9. Science

    A person roller skates down a street heading West. What is true about friction in this case?
  10. science

    a person roller skates down a street heading east which of the following would be true abot friction in this scenario?

More Similar Questions