Download Physics test review ANSWER KEY

Physics test review
ANSWER KEY
Draw free body diagrams for each of the following situations, the find the requested information.
NOTE: I am currently planning to stay after school on Tuesday to review any of these problems in more
detail. This is, of course, subject to change.
1. A 35 kg crate rests on a horizontal floor and a 65 kg person is standing on the crate. Determine the
magnitude of the normal force provided by the floor on the crate, and the normal force of the crate
on the person.
Normal force of crate on person = 637 N
Normal force of floor on crate = 980 N
2. A rocket blasts off from rest and attains a speed of 45 m/s in 15 s. An astronaut has a mass of 57
kg. What is the astronaut’s apparent weight during takeoff?
730 N
3. A 95 kg person stands on a scale in an elevator. What is the apparent weight of the person when
the elevator is:
a. moving upward with an acceleration of 1.8 m/s2?
1102 N
b. moving upward with a constant velocity of 2 m/s?
931 N
c. moving downward with a constant velocity of 1.5 m/s?
931 N
d. moving downward with an acceleration of 1.30 m/s2?
788.5 N
4. A 60 kg crate rests on a level floor at a shipping dock. The coefficients of static and kinetic friction
are 0.760 and 0.410 respectively. What horizontal force is required to:
a. just start the crate moving?
447 N
b. slide the crate across the floor at a constant speed?
241 N
c. give the crate an acceleration of 0.15 m/s2?
250 N
5. A sled is traveling at 4.00 m/s along a horizontal stretch of snow. The coefficient of kinetic friction
is 0.0500. How far does the sled go before stopping?
16.3 m
6. A flatbed truck is carrying a crate up a 10.0° hill. The coefficient of static friction between the truck
bed and the crate is 0.350. Find the maximum acceleration that the truck can attain before the
crate begins to slip on the truck bed.
1.68 m/s2
7. A 92 kg baseball player slides into second base. The coefficient of kinetic friction between the
player and the ground is 0.61.
a. What is the magnitude of the frictional force?
550 N
b. If the player comes to rest in 1.2 seconds, what was his initial speed?
7.17 m/s
Physics test review
ANSWER KEY
Draw free body diagrams for each of the following situations, the find the requested information.
NOTE: I am currently planning to stay after school on Tuesday to review any of these problems in more
detail. This is, of course, subject to change.
8.
A 250-kg crate is initially moving at 3.0 m/s. Find the force of friction acting on the crate to stop it
if the coefficient of kinetic friction is 0.65.
1593 N
9. A 30-kg box is at rest on a wooden floor (μs = 0.50).
a. What horizontal force is necessary to just start the box in motion?
147 N
b. If a force of 91 N is continuously applied once the box is in motion, what will be its
acceleration (μk = 0.30)?
0.093m/s2
10. A 0.50-N eraser is held against a whiteboard with an applied force of 6.00 N. What must be the
coefficient of static friction between the eraser and the board such that the eraser will remain at
rest?
0.083
11. A man is pulling his daughter in a sled. The daughter and sled have a combined mass of 40 kg. The
man applies a force of 95 N at an angle of 30˚ above the horizontal.
a. If the force of friction is 25 N, what is the acceleration of the daughter and sled?
1.43 m/s2
b. What is the normal force acting on the sled?
344.5 N
12. A 20 kg block slides down a smooth (frictionless) plane. The plane is 10.0 m long and inclined at an
angle of 30˚ above the horizontal. Find:
a. the acceleration of the block
4.9 m/s2
b. the velocity of the block at the bottom of the plane.
9.89 m/s