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A0.5kg teddy bear is nudged off a window sill and falls 2m to the ground. (a) What is the kinetic energy at the instant it hits the ground? What is its speed? What assumptions or approximations did you make in this calculation?

(b) A 1.0kg flowerpot is nudged off a window sill and falls 2m to the ground. What is the kinetic energy at the instant it hits the ground? What is its speed? How do the speed and kinetic energy compare to that of the teddy bear in part (a)?

Short Answer

Expert verified

(a) For 0.5kg teddy bear,

The speed is6.26m/s

The kinetic energy at the instant it hits the ground is 9.80J

(b) For1.0kg flowerpot

The speed is 6.26m/s

The kinetic energy at the instant it hits the ground is 19.59J

Step by step solution

01

Identification of given data

- The mass of a teddy bear is 0.5kg

- The height from which the teddy bear falls is 2m

- The mass of a flowerpot is 1.0kg

- The height from which the flowerpot falls is 2m

02

concept of kinetic energy

The kinetic energy is determined when an object is in motion. When the total force is applied on an object, the work done speeds up the object and gets kinetic energy.

03

(a) Calculation of Speed and kinetic energy of a teddy bear

The speed is calculated by the following formula,

v2=2gH

where,

g=acceleration due to gravity =9.81m/s2

H=height from which the teddy bear falls

Substitute the values in the above expression,

v=2gH

=2×9.81×2

=6.26m/s

Hence, the speed of a teddy bear is 6.26m/s

The kinetic energy is calculated by the following formula,

E=12mv2

where,

m=mass of a teddy bear

v-speed of a teddy bear

Substitute the values in the above expression,

E=12×0.5×6.262

=9.80J

Hence, the kinetic energy at the instant the bear hits the ground is 9.80J

The approximation and assumption made in this calculation is the "g" value which is due to the acceleration of gravity.

04

(b) Calculation of Speed and kinetic energy of a flowerpot

The speed is calculated by the following formula,

v2=2gH

where,

g=acceleration due to gravity =9.81m/s2

H=height from which the teddy bear falls

Substitute the values in the above expression,

v=2gH

=2×9.81×2

=6.26m/s

Hence, the speed of a teddy bear is 6.26m/s

The kinetic energy is calculated by the following formula,

E=12mv2

Where,

m=mass of a teddy bear

v-speed of a teddy bear

E=12×1×(6.26)2

=19.59J

Hence, the kinetic energy at the instant the bear hits the ground is 19.59J

The speed of a flowerpot and the bear is the same because both of them fall from the same height H.

The kinetic energy of a flower pot is twice of that of a teddy bear. Because the mass of the flowerpot is twice as the mass of a teddy bear.

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http://www.jpl.nasa.gov/sl9/ sl9.html

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