FBDs
A book rests motionless on a horizontal table. Name all forces acting on the book and their directions.
Normal force upward and gravitational force downward.
Two blocks are connected by one ideal string over an ideal pulley. If block A accelerates at 3 m/s2 what is the magnitude of block B's acceleration?
3 m/s2
A block sits on a ramp at an angle theta. Gravity has a component parallel to the ramp.
What is the equation (in variable form) of the parallel component of the gravity.
mg*sin(theta)
A lamp hangs motionless from one vertical string. If the lamp weighs 50N, what is the tension?
50N
Complete the equation: F =
ma
A person pulls a box to the right across a frictionless floor using a horizontal rope. Draw the FBD for the box.
Fg down, FN up, tension right.
A 2kg hanging block accelerates downward at 2 m/s2. Write Newton's 2nd Law equation for the block if downward is positive.
mg - T = ma
A block sits on a ramp at an angle theta. Gravity has a component parallel to the ramp.
What is the equation (in variable form) of the perpendicular component of gravity.
mg*cos(theta)
A 10KG object hangs motionless from two identical vertical ropes that share the load equally. Find the tension in each rope.
2T = mg
T = 49N
T or F: If an object is not moving, there are no forces acting on it.
False. the forces may balance
A block slides down a frictionless ramp. What forces belong on its FBD?
Gravity and normal force.
A 5 kg block sits on a frictionless table and is connected over a pulley to a hanging 2 kg block.
Which block provides the force that causes the system to accelerate?
The hanging 2kg block, specifically its gravitational force (weight).
A 10 kg block sits on a frictionless 30 degree incline. Find the component of gravity parallel to the ramp.
A ball hangs motionless from a string at an angle. When resolving the tension into components, which trig functions will generally be needed?
sine & cosine
T or F: If an object moves at constant velocity, the net force acting on it is zero.
True
A block hangs motionless from a vertical rope. What can you conclude about the tension compared with the block's weight?
T = mg
A 5 kg block sits on a frictionless table and is connected over a pulley to a hanging 2 kg block.
Find the acceleration of the system.
m2g = (m1 + m2)a
a = (2 * 9.81) / 7 = 2.8 m/s2
A block slides down a frictionless 30 degree incline. Determine its acceleration.
mgsin(theta) = ma
a = gsin(30) = 4.9 m/s2
A 10kg road sign is supported by two identical ropes. Each rope makes a 30 degree angle above the horizontal.
Write the vertical equilibrium equation.
2T*sin(30) - mg = 0
Find the net force of a 4kg object that accelerates at 3m/s2 to the right.
F = ma = (4 * 3) = 12N
A student draws an FBD for a box being pulled across the floor and includes:
What is wrong with their FBD?
Acceleration is not a force and shouldn't appear on the FBD.
A 5 kg block sits on a frictionless table and is connected over a pulley to a hanging 2 kg block.
find the tension in the string.
T = m1a
T = (5 * 2.8) = 14N
Two blocks of masses 5kg and 10kg are released separately on the same frictionless ramp.
Which block accelerates faster? Why?
Neither. They have the same acceleration.
A 10kg road sign is supported by two identical ropes. Each rope makes a 30 degree angle above the horizontal.
Calculate the tension in each rope.
2T*sin(30) = mg
T = 98N
A box has:
Determine the magnitude and direction of its acceleration.
Fnet = 30 - 18 = 12N
a = 12 /4 = 3m/s2