science question?

Question

please help me by answering the questions below and explain the steps so i can make sure i did these right.
thnk you.!!

A.) maria consumes 75 kijoules of energy froma candy bar. if only 30 percent is lost as waste heat, how much energy can be used for actual work.?

B.) a 5000kg truck travels north in I-95 at a velocity of 108 kilometers per hour. whats the momentum at that velocity?

Answer 1

A)
75kJ = 75,000J
75,000*(0.3) = 22,500J which is what is lost as heat.

75,000 - 22,500 = 52,500J that can be used as work.



B)
Momentum (p) = mass*velocity
mass = 5000kg
velocity = 108km/hr = 108000meters/hr. To convert meters per hour into meters per second, divide by 3600 because that's how many seconds are in an hour.

108000meters * 1hr/3600 seconds = 30m/s

p = (30)(5000) = 150,000 kg*m/s

Answer 2

Hmmm.

The first question is easy. Do you know what 70% of 75 is?

The second is easy as long as you know what units to use.

Momentum, p, equals mass * velocity, or p = m v

To use this equation, you have to be in SI units, kg for mass, meter for length and second for time.

So you have to convert 108 km/hr to m/s.

108 km/hr x 1000 m/km x 1 hr/3600s = 30 m/s

Thus p = 5000 kg * 30 m/s = 150 x 10^3 kg m/s

Answer 3

kiJ ? whats a kiJ? Slopheeheeheehee.
30% is waste that leaves 70% as not waste (useful)
70% of 75 is = 0.7*75 = you do the math

momentum = mass * velocity ::: memorize it.
also need to know standard units usually kg*m/s
so
1. put everything into standard units - the velocity is the issue
2. solve the equation.

Answer 4

a) 52.5 kilijoules