Chapter 15 - Energy Transfers Flashcards
1
Q
efficiency =
A
useful energy output / total energy
input
2
Q
A man of mass 78kg
Height of 5.0m
Show that the gravitational potential energy gained by the man is about 4000J
A
78 x 5 x 10
= 3900J
3
Q
An escalator lifts 30 people each minute
Escalator is powered by a 7.5kW electrical motor
Each person has a man of 78kg
Work done = 3900J
A
useful energy output / total energy input useful energy out = (3900 x 30) / 60 = 1950 useful energy input = 7500 1950/7500 = 26%
4
Q
State one way in which a student could increase the efficiency of heating the aluminium block. [1 marks]
A
insulate the block
5
Q
State the relationship between momentum, mass and velocity (1)
A
momentum = mass x velocity
6
Q
The mass of a car is 900kg. The max speed of the car is 15 m/s. Calculate the max momentum of the car (3)
A
900 x 15 = 13500 kg m/s
