Conceptual questions
What happens to an object's acceleration if the net force acting on it is zero?
a = 0 m/s2 - the object remains at rest or with constant acceleration
A runner travels at a constant velocity of 6.0 m/s for 12 s. Find the displacement
72 m
A hiker walks 6.0 km east and then 8.0 km north. Find the magnitude and direction of the resultant vector.
10 km at 53° north of east
A 50 N force pushes a box 8.0 m at an angle of 30° above the horizontal. Find the work done by the force.
346 J
What direction does centripetal acceleration always point?
Towards the center of the circle
What is the difference between distance and displacement?
Distance: total path traveled
Displacement: change in position
A car travels 2.40×104 m in 8.0 min. Find its average speed in:
a. m/s
b. km/h
50 m/s and 180 km/h
A 12 kg box is pulled horizontally with 60 N on a frictionless surface. Draw a free body diagram and find
a. Net force
b. Acceleration
c. Normal force
60 N to the right, 5 m/s2 to the right, 117.6 N upward
A 1200 kg car travels around a curve of radius 50 m at 15 m/s. Find:
a. Centripetal acceleration
b. Centripetal force
4.5 m/s2 and 5400 N
A car starts from rest and accelerates at 4.0 m/s2 for 10 s. Find:
a. Final velocity
b. Displacement
vF = 40 m/s and s = 200 m
A roller coaster starts at rest at the top of a hill and moves down a frictionless track. Explain how energy changes throughout the motion.
As it moves down PE decreases and KE increases. At the bottom of the track the roller coaster will only have KE.
A cyclist is traveling at 4.0 m/s and accelerates at 1.5 m/s2 until reaching 10.0 m/s. Find:
a. Time required
b. Distance traveled
4 s and 28 m
A ball is launched horizontally from a 45 m cliff at 12 m/s. Find:
a. Time in the air
b. Horizontal distance
c. Vertical velocity just before impact
3.03 s, 36.4 m and 29.7 m/s downward
A spring has a spring constant of 250 N/m. A student stretches the spring 0.080 m from its equilibrium position. Find:
a. The magnitude of the spring force acting on the student’s hand.
b. If the spring is stretched to 0.120 m, what is the new spring force?
c. How much does the spring force increase when the displacement changes from 0.080 m to 0.120 m?
20.0 N, 30.0 N and 10.0 N
A 0.50 kg ball moves in a circle of radius 1.2 m. If the centripetal force is 15 N, find its speed.
6 m/s
Ignoring air resistance, why does the horizontal velocity of a projectile remain constant?
There is no horizontal force acting upon the object
A motorcycle starts from rest and accelerates at 4.0 m/s2 for 5.0 s. It then brakes with an acceleration of −2.0 m/s2 until it stops. Find:
a. Maximum velocity
b. Time spent braking
c. Total distance traveled
20 m/s, 10 s and 150 m
A 10 kg block slides down a 30° frictionless incline. Draw a free body diagram and find:
a. Gravitational force parallel to the incline
b. Normal force
c. Acceleration
49 N, 84.9 N and 4.9 m/s2
A 1200 kg car accelerates from 10 m/s to 25 m/s. Find:
a. Initial kinetic energy
b. Final kinetic energy
c. Change in kinetic energy
d. If this change occurs in 8.0 s, find the average power delivered to the car.
6.0 x 104 J, 3.75 x 105 J, 3.15 x 105 J, and 3.9 x 104 W
A box is pulled horizontally across a rough surface at constant velocity. What can you conclude about the net force?
Constant velocity = no acceleration (a = 0)
No acceleration (a = 0) then no net force (Fnet = 0) by F = ma
A projectile is launched at two different angles with the same initial speed. Under what conditions can the two projectiles have the same horizontal range?
When they are launched at complementary angles (Ex. 30° and 60°)
A ball is dropped from a 50 m cliff. At the same instant, another ball is thrown upward from the ground at 20 m/s. Determine whether (and where) the two balls meet before the first ball reaches the ground.
19 m above the ground
A kayak moves 5.0 km at 35° north of east, followed by 8.0 km east, and then 7.0 km at 30° south of east. Find the magnitude and direction of the resultant vector.
18 km at 2.0° south of east
A 1500 kg car travels around a banked curve with a radius of 120 m. The road is banked at 18°. The coefficient of static friction between the tires and the road is μs = 0.40. Find:
a. The normal force acting on the car at the speed in which the car will not skid
b. The ideal speed at which the car can travel around the curve without relying on friction
c. The frictional force acting on the car at said ideal speed
1.5 x 104 N, 20 m/s and 0 N
A person pushes a heavy box but it does not move. Is the person doing work on the box?
No displacement = no work