Physics
Work and Energy
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#49 If constant power acts on a mass, its speed varies as:
A) $v\propto t^{1/2}$
B) $v\propto t$
C) $v\propto t^{2}$
D) $v\propto t^{0}$
#50 Energy stored in a spring stretched by $x$ is:
A) $kx^2$
B) $\tfrac12 kx^2$
C) $k/x$
D) $kx$
#51 A constant force $F=5\,\text{N}$ acts through $s=4\,\text{m}$ at $\theta=120^\circ$. The work done is:
A) $Fs$
B) $F+s$
C) $F/s$
D) $5s\,\cos120^\circ$
#52 A constant force $F=5\,\text{N}$ acts through $s=4\,\text{m}$ at $\theta=90^\circ$. The work done is:
A) $Fs$
B) $F/s$
C) $F+s$
D) $0$
#53 For a conservative force, the potential energy function $U$ satisfies:
A) $\vec F=+\nabla U$
B) $\nabla\cdot\vec F=U$
C) $\vec F=-\nabla U$
D) $\nabla\times\vec F=\nabla U$
#54 Instantaneous power delivered by a constant force is:
A) $P=F^2v$
B) $P=Fv\sin\theta$
C) $P=F/v$
D) $P=\vec F\cdot\vec v$
#55 A constant force $F=10\,\text{N}$ acts through $s=2\,\text{m}$ at $\theta=120^\circ$. The work done is:
A) $10s\,\cos120^\circ$
B) $F/s$
C) $F+s$
D) $Fs$
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