Energy 2

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1. What are the S.I. and base units for power? Answer
P = W/Δt
Now W = F.Δx
and F = ma
Thus W = maΔx

P = max/t

in units:

P = kg.m.s-2m/s
P = kg.m2s-3

2. An engine is marked 100kW. What does this mean? Answer
The engine can develop 100kJ of energy in a time of 1 second.
3. A car, moving at constant velocity with kinetic energy Ek, undergoes a displacement x in time t. If the car's kinetic energy changes to a value of 2Ek, then in the same time, at the new constant velocity, it will undergo a displacement of …

A. 4x
B. 2x
C. 1,414x
D. 0,707x

8. For an object thrown vertially upwards, which statement is true when it reaches its highest point?

A. Ep = Ek
B. acc = 0
C. p = 0
D. Em = 0

v = 0, hence p = 0.
5. Why must the kinematic equations of motion not be used to solve “pendulum” problems? Answer
The curve of the pendulum movement would mean that the acceleration would not be constant due to the changing direction.
Kinematic equations are valid only for constant accelerations.

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