Circular Motion
The formula for centripetal acceleration.
ac = v^2/r
A ball is thrown straight up. At the very top, what is its velocity? Its acceleration?
v = 0, a = -g
A truck and a tennis ball have the same speed. Which has more momentum?
Truck.
Definition of work. (Explain what the dot product is as well.)
W = F dot x = (mag F)*(mag x)*cos(theta)
A roller coaster car goes through a loop-the-loop. At the very top of the loop, which forces act on the car? (Not on the verge of falling)
Normal force and gravity.
Difference between conservative and non-conservative force.
Non-conservative: path dependent, all other forces
The condition in which momentum is conserved.
No external force on the system.
A student carries a backpack across the room at constant height. How much work does gravity do on the backpack?
0
A ball is moving in a perfect circle at constant speed.
Is the ball accelerating?
Yes, the velocity changes direction constantly.
A book sits on a table. Does it have gravitational potential energy?
Relative to what?
If 0 at table, then no Ug.
If 0 at ground, then yes Ug.
A rifle fires a bullet forward. What happens to the rifle?
A block is pulled with 50 N across 10 m of rough floor. Friction force = 20 N. What is the net work done on the block?
500-200 = 300
A ball on a string is whirled in a horizontal circle.
The string suddenly breaks. What path does the ball follow immediately after the break?
Perpendicular to radius.
A block slides down a frictionless ramp and compresses a spring. Where is the kinetic energy maximum?
A. top of ramp
B. bottom of ramp before spring
C. maximum spring compression
A car and truck collide head on and stick together. Which undergoes a larger momentum change?
Impulse-momentum formula. Same for both.
You push harder on a box, but it still doesn’t move. How does the work done change?
No work is done no matter what
At the bottom of a roller coaster loop, which force is larger: gravity/normal force
Normal force.
Two balls are dropped at same height, Ball A with mass 2 kg, Ball B with mass 4 kg. Ignoring air resistance: Which hits the ground with greater speed?
Same speed.
mgh = (1/2)mv^2
v = sqrt(2gh)