Question
A car is moving along a straight horizontal road. The car has $1.6 \mathrm{MJ}$ of kinetic energy. The car accelerates for $20 \mathrm{~s}$ until the kinetic energy of the car increases to $2.5 \mathrm{MJ}$.
What is the minimum average power developed by the car engine for this acceleration?
A $45 \mathrm{~W}$
B $205 \mathrm{~W}$
C $45 \mathrm{~kW}$
D $205 \mathrm{~kW}$
Answer/Explanation
Ans:C
Question
A crane is used to lift loads vertically.
The output power of the crane to lift a car is P.
The crane then lifts a lorry, which has 3.0 times the weight of the car, through 0.25 of the distance in 0.50 of the time.
What is the output power of the crane now?
A
B
C
D 6P
Answer/Explanation
Ans: B
Question
crane takes 2.0 minutes to lift a load to the top of a building. The change in gravitational
potential energy of the load is 360 kJ.
What is the useful power output of the crane?
A 3.0 kW
B 180 kW
C 720 kW
D 43 200 kW
Answer/Explanation
Ans: A
Question
A weight-lifter raises a 2000 N weight through a vertical height of 2.0 m in 0.80 s.
What useful power does he develop in doing this?
A 800 W
B 3200 W
C 4000 W
D 5000 W
Answer/Explanation
Answer/Explanation
Ans: D
Question
A girl hangs by her hands from a bar in the gymnasium. She pulls herself up until her chin is level
with the bar. The mass of the girl is 48 kg.
She pulls herself up through a distance of 0.25 m. She does this in 2.0 s.
What is the useful power she uses to pull herself up?
A 6.0 W
B 24 W
C 60 W
D 240 W
Answer/Explanation
Ans: C