Force
Chapter 5
Formulae
Name: ____________________
Friday, October 31, 2014
d = vi t + ½ a t2
d = ½ (vf + vi) t
A.
vf2 = vi2 + 2 a d F = m a
vf = vi + a t
g = 9.81 m/s2
Ff =  FN
FREE-BODY DIAGRAMS
2
Draw and label vectors a free-body diagram showing the forces acting on you:
when the elevator begins to go down (↓)
you are sliding forward (→) on concrete
B.
DESCRIBING MOTION USING THE LAWS OF MOTION
A teddy bear wearing an open parachute was dropped from the top of a tall building.
 Use your knowledge of the laws of motion to explain the motion of the teddy bear
immediately after it was released until just before it lands
 Use each of the three laws of motion at least once to describe the motion of the teddy bear.
3
C.
CHOICE
WRITE THE BEST WORD FOR EACH STATEMENT
3
1.
(FRICTION / NORMAL ) force always acts parallel to the surface of contact.
________________
2.
The apparent weight of an object (DECREASES / INCREASES) when it comes to stop while moving upward.
________________
3.
When you are driving, you want ( KINETIC / STATIC ) friction acting between your tires and the road.
________________
D.
MULTIPLE CHOICE
WRITE THE LETTER (A, B, C, OR D) OF THE BEST ANSWER FOR EACH STATEMENT.
2
_____ 1. An object that weighs 49 N on Earth is taken to the Moon where the acceleration due to gravity is 1.6 m/s2.
The mass of the object on the moon is
A. 1.6 N
B. 5.0 kg
C. 8.0 N
D. 30.6 kg
_____ 2. A 75.0 kg snowboarder on a frictionless steep hill that is inclined at 65 from the horizontal.
The net force downhill is
A. 4.14 N
B. 311 N
C. 667 N
D. 736 N
_____ 3. A brick on a table has inertia. Which one of the following best identifies the inertia of the brick?
A. It is the ratio of its weight to its momentum.
B. It is the resistance to moving resulting from its mass.
C. It is the force of friction resulting from its momentum.
D. It is the force of friction resulting from its normal force.
E.
DEFINITIONS
1. Force
2. Impulse
DEFINE BOTH TERMS
[2]
F.
WORD PROBLEMS
BEST 4 (EXTRA  BONUS)
1. A base cheerleader exerts a force of 1150 N when lifting a 50.0 kg top cheerleader.
(a)
Find the net force upward of the top cheerleader during the lift. [2]
(b)
Find the upward acceleration of the top cheerleader during the lift. [2]
4 POINTS EACH = [16]
_____________
_____________
2. A 60-kg woman is standing on a scale in an elevator. What is the reading on the scale (in newtons):
(a)
when the elevator moving downward slows down and stops at a rate of 2.0 m/s2.[2]
_____________
(b)
when the elevator accelerates at 3.0 m/s2 as it starts moving up. [2]
_____________
3. A 57-g tennis ball moving at 20.0 m/s hits a wall and bounces away at 15.0 m/s. The ball was touching to wall for 0.020 s.
(a) What was the change of momentum of the tennis ball? [2]
_____________
(b) What was the average force exerted by the wall on the ball? [2]
_____________
4. A parent exerts a force of 50.0 N to pull two children on a toboggan with a constant velocity of 2.5 m/s along a flat, perfectly
horizontal field. The children and toboggan have a combined mass of 80.0 kg. Find:
(a)
the weight of the children and the toboggan. [1]
_____________
(b)
the force of friction. [2]
_____________
(c)
the coefficient of sliding friction between the toboggan and the snow. [1]
_____________
5. A 250-gram cart on a horizontal track is attached to a 30.0-gram object that is suspended over a pulley. (Newton’s 2nd Law Lab)
(a)
Find the acceleration of the cart if the system is frictionless. [2]
_____________
(b)
How much time did it take the cart moving to travel 0.65 m? [2]
_____________
6. A 7.35 kg brick is on a track that is inclined at an angle of 10.0° to the horizontal.
A force of 7.50 N is required before it starts to move down the ramp. (Friction on an Incline Lab)
(a)
Find the coefficient of friction between the brick and the track [4]
_____________