A resultant force of $10\,\text{N}$ acts on a $2.0\,\text{kg}$ mass. What is its acceleration?
$5.0\,\text{m s}^{-2}$
$20\,\text{m s}^{-2}$
$0.2\,\text{m s}^{-2}$
$12\,\text{m s}^{-2}$
Tap an answer to check it.
WhyBy Newton's second law $a=\frac{F}{m}=\frac{10}{2.0}=5.0\,\text{m s}^{-2}$.
2Multiple choice · Easy
A car of mass $1500\,\text{kg}$ moves at $20\,\text{m s}^{-1}$. What is its momentum?
$3.0\times 10^{4}\,\text{kg m s}^{-1}$
$75\,\text{kg m s}^{-1}$
$1500\,\text{kg m s}^{-1}$
$3.0\times 10^{5}\,\text{kg m s}^{-1}$
Tap an answer to check it.
WhyMomentum $p=mv=1500\times 20=3.0\times 10^{4}\,\text{kg m s}^{-1}$.
3Multiple choice · Medium
A constant force of $50\,\text{N}$ acts for $0.20\,\text{s}$. What is the impulse delivered?
$10\,\text{N s}$
$250\,\text{N s}$
$0.40\,\text{N s}$
$50\,\text{N s}$
Tap an answer to check it.
WhyImpulse $=F\Delta t=50\times 0.20=10\,\text{N s}$, equal to the change in momentum.
4Multiple choice · Hard
A $2.0\,\text{kg}$ trolley moving at $3.0\,\text{m s}^{-1}$ collides with and sticks to a stationary $1.0\,\text{kg}$ trolley. What is their common velocity afterward?
$2.0\,\text{m s}^{-1}$
$3.0\,\text{m s}^{-1}$
$1.5\,\text{m s}^{-1}$
$6.0\,\text{m s}^{-1}$
Tap an answer to check it.
WhyConserving momentum: $2.0\times 3.0=(2.0+1.0)v$, so $v=\frac{6.0}{3.0}=2.0\,\text{m s}^{-1}$.
5Multiple choice · Medium
A $0.50\,\text{kg}$ ball moves in a circle of radius $2.0\,\text{m}$ at $4.0\,\text{m s}^{-1}$. What centripetal force is required?
A book rests on a table. According to Newton's third law, the reaction to the book's weight (Earth pulling book) is:
The book gravitationally pulling the Earth upward
The table pushing up on the book
The book pushing down on the table
The normal force on the table
Tap an answer to check it.
WhyNewton's third law pairs act on different bodies and are the same type of force. The reaction to Earth pulling the book is the book pulling the Earth (gravitational).
7Fill in the blank · Easy
The product of a force and the time for which it acts is called the .
Answer:
impulse
WhyImpulse $=F\Delta t$, which equals the change in momentum $\Delta p$.
8Fill in the blank · Medium
The total momentum of a system is conserved when the net external force on it is .
Answer:
zero / 0
WhyConservation of momentum follows from Newton's laws: with zero net external force, $\frac{\Delta p}{\Delta t}=0$.
9Multiple choice · Medium
A block of mass m slides down a smooth plane inclined at angle theta to the horizontal. The net force along the plane is
mg sin theta
mg cos theta
mg
mg tan theta
Tap an answer to check it.
WhyThe component of weight along the plane is mg sin theta, the only force along a frictionless plane.
10Multiple choice · Medium
On a frictionless incline of angle theta, the acceleration of a sliding object is independent of
its mass
the angle of the incline
the gravitational field strength
the value of g
Tap an answer to check it.
WhyFrom a = g sin theta, the acceleration does not depend on the mass of the object.
Ready to test yourself?
Practise Forces and momentum with instant marking and per-topic score tracking.