Question

It is 7.0 km from your home to the physics lab. As part of your physical fitness program, you could run that distance at 10 km/h (which uses up energy at the rate of 700 W), or you could walk it leisurely at 3.0 km/h (which uses energy at 290 W).
Required:
a. Which choice would burn up more energy, and how much energy (in joules) would it burn?
b. Why does the more intense exercise burn up less energy than the less intense exercise?

Answer 1

Answer:

a. the second choice of leisurely walking at 3 km/h burn up more energy, which is equal to 2.436 MJ

b. Due to more time

Explanation:

a.

FOR 10 km/h SPEED:

First, we find time taken to reach physics lab:

S₁ = V₁t₁

t₁ = S₁/V₁

where,

t₁ = time = ?

S₁ = Distance = 7 km

V₁ = Speed = 10 km/h

Therefore,

t₁ = (7 km)/(10 km/h)

t₁ = (0.7 h)(3600 s/1 h) = 2520 s

Now, we calculate the energy burnt:

P₁ = E₁/t₁

E₁ = P₁ t₁

where,

E₁ = Energy Burnt = ?

P₁ = Power Used = 700 W

t₁ = 2520 s

Therefore,

E₁ = (700 W)(2520 s)

E₁ = 1.764 MJ

FOR 3 km/h SPEED:

First, we find time taken to reach physics lab:

S₂ = V₂t₂

t₂ = S₂/V₂

where,

t₂ = time = ?

S₂ = Distance = 7 km

V₂ = Speed = 3 km/h

Therefore,

t₂ = (7 km)/(3 km/h)

t₂ = (2.333 h)(3600 s/1 h) = 8400 s

Now, we calculate the energy burnt:

P₂ = E₂/t₂

E₂ = P₂ t₂

where,

E₂ = Energy Burnt = ?

P₂ = Power Used = 290 W

t₂ = 8400 s

Therefore,

E₂ = (290 W)(8400 s)

E₂ = 2.436 MJ

Hence, the second choice of leisurely walking at 3 km/h burn up more energy, which is equal to 2.436 MJ

b.

The more intense exercise burn up less energy than the less intense exercise, because it is performed for a longer period of time.