Power AP Physics 1 MCQ – Exam Style Questions etc.
Power AP Physics 1 MCQ
Unit: 3. Work , Energy and Power
Weightage : 10-15%
Exam Style Practice Questions, Power AP Physics 1 MCQ
Question
A pile of bricks of mass M is being raised to the tenth floor of a building of height H = 4y above the ground by a crane that is on top of the building. During the first part of the lift, the crane lifts the bricks a vertical distance \(h_1=3y\) in a time \(t_1=4T\). During the second part of the lift, the crane lifts the bricks a vertical distance \(h_2=y\) in \(t_2=T\). Which of the following correctly relates the power \(P_1\) generated by the crane during the first part of the lift to the power \(P_2\) generated by the crane during the second part of the lift?
A \(P_2=4P_1\)
B \(P_2=\frac{4}{3}P_1\)
C \(P_2=P_1\)
D \(P_2=\frac{3}{4}P_1\)
E \(P_2=\frac{1}{3}P_1\)
Answer/Explanation
Ans:B
Using the equation for power for the first part of the lift, \(P_1=\frac{W}{t}=\frac{mgh}{t}=\frac{mg(3y)}{(4T)}=\frac{3mgy}{4T}\) . For the second part of the lift, \(P_2=\frac{W}{t}=\frac{mgh}{t}=\frac{mg(y)}{(T)}=\frac{mgy}{T}\); thus, \(P1=\frac{3mgy}{4T}=\frac{3}{4}P_2\rightarrow P_2=\frac{4}{3}P_1\)Question
A wheel with rotational inertia I is mounted on a fixed, frictionless axle. The angular speed 𝜔 of the wheel is increased from zero to 𝜔𝑓 in a time interval T.
What is the average power input to the wheel during this time interval?
A \(\frac{Iω_f}{2T}\)
B \(\frac{Iω_f^2}{2T}\)
C \(\frac{Iω_f^2}{2T^2}\)
D \(\frac{I^2ω_f}{2T}\)
E \(\frac{I^2ω_f^2}{2T^2}\)
Answer/Explanation
Ans:B