Tuesday

November 25, 2014

November 25, 2014

Posted by **Ali** on Saturday, October 22, 2011 at 12:30am.

(a) How much potential energy does it have? (b) How much kinetic energy does it have?

(c) The block is raised to 2m high. How much potential energy does it have? (d) The block is raised to 4m high. How much potential energy does it have?

(e) The block is raised to 45m high. How much potential energy does it have? (f) The block is dropped to the ground. How fast is it traveling when it hits the ground? (remember chapter 2?)

(g) How much kinetic energy does it have when it hits the ground?

- science -
**Jai**, Saturday, October 22, 2011 at 2:40am(a)

recall that potential energy is stored energy, and is given by the formula:

PE = mgh (units in Joules)

where

m = mass (in kg)

g = acceleration due to gravity = 9.8 m/s^2

h = height (in m)

if the reference position is at the floor (that is, h = 0), the PE is equal to

PE = 4*9.8*0

PE = 0

(b)

recall that kinetic energy is energy in motion and is given by the formula:

KE = (1/2)*m*v^2

where

v = velocity (in m/s)

since it's not moving (v = 0),

KE = 0

(c)

at 2 m high,

PE = 4*9.8*2

PE = 78.4 J

(d)

at 4 m high,

PE = 4*9.8*4

PE = 158.8 J

(e)

at 45 m high,

PE = 4*9.8*45

PE = 1764 J

(f)

recall that the motion of the block is uniformly accelerated motion, and we can therefore use the formula:

(v,f)^2 - (v,o)^2 = 2gh

where

v,f = final velocity (in m/s)

v,o = initial velocity (in m/s)

since it is dropped from rest, v,o = 0:

v,f^2 = 2gh

v,f = sqrt(2gh)

v,f = sqrt(2*9.8*45)

v,f = 29.7 m/s

(g)

KE = (1/2)mv^2

KE = (1/2)*4*29.7^2

KE = 1764.18 J

this actually shows the law conservation of energy, which is ΔPE = -ΔKE

hope this helps~ :)

**Answer this Question**

**Related Questions**

Physics - A horizontal force of magnitude 30.0 N pushes a block of mass 3.85 kg ...

science - 1. How much potential energy does a 5kg block have if it is 2m above ...

physics - A block is initially sliding along a horizontal surface with 24.6 J of...

physics - A gun is fired vertically into a 1.55 kg block of wood at rest ...

physics - A small block of mass m = 225 g is released from rest at point circled...

Physics ~Conservation of Energy~ part 2 - 1.) A 500 kg roller coaster is pulled ...

physics - A block is moving down an incline a distance of 5 m form point A to ...

Science - A lead bullet with a mass of 8.50 g traveling at 4.80 x 102 m/s ...

physics - A bullet with mass m = 5.21 g is moving horizontally with a speed v=...

Physics - drwls? - A small block of mass m = 4.0 kg can slide along the ...