Test corrections Energy

Question 1

42. What is the potential energy of a puppy who weighs 18 N sitting in a high chair 2 m high

Answer 1

Given GPE = FH
H = 2 m GPE = 18 * 2
a = 9.8 GPE = 36 J
F = 18 N

Question 2

44. An 8 kg toddler is running using 400 J of kinetic energy. What is the velocity of the child

Answer 2

Given            V2 = KE / 1/2m2
m = 8 kg        V2 = 400/ 1/2 *82
KE = 400 J     V2 = 400/4
V = ?               V2 = 100
                         V = 10 m/s

Question 3

45. Justin kicks a football straight up during a game. Assuming all energy is conserved, at what height did the 2.6 kg ball travel if it had a velocity of 6 m/s?

Answer 3

Given
m = 2.6 kg
V = 6 m/s
a = 9.8
H = ?

KE = 1/2 mv2
KE = GPE
GPE = Ham
F = ma

KE = 1/2 * 2 * 6 * 36
KE = 46.8 J
GPE = 46.8 J
H = GPE/F
F = 2.6 * 9.8
H = 46.8/25.4
H = 1.8 m

Question 4

48. A recycling center is melting down gold. It starts out at 18°C and reaches its melting point at 108°C by absorbing 153,000 J of energy. What was the mass of the melted gold? Note: Gold has a specific heat of 136 J/kg/°C.

Answer 4

Given
Ti = 18 °C
Tf = 108 °C
Q = 153,000 J
C = 136 J/kg/°C

m = Q/ C^t

m = 153,000/136 * 90
m =  153,000/12,240
m = 12.5 kg

Question 5

52. A piece of zinc was laying outside and had a temperature of 26°C. Later that day the sun came out and the heat increased to 36°C. If the piece of zinc was only 0.15 kg, find the thermal energy. Note: Zinc had a specific heat of 380 J/kg/°C

Answer 5

Given
Ti = 26°C
Tf = 36°C
m = 0.15 kg
c =  380 J/Kg°C

Q = mc(Tf - Ti)
Q = .15 * 380 (36 - 26)
Q =  57 ( 10)
Q = 570 J

Question 6

What unit is used to measure force

Answer 6

N = Newton’s unit 6