Download 8th Grade Science

Physics Study Guide Force
1. A 300-N force acts on a 25-kg object. The acceleration of the object is ____.
2. A 3,000-N force acts on a 200-kg object. The acceleration of the object is____.
3. A 105.0 kg boxer has his first match in Panama (g=9.782 m/s2) and his second match at the
North Pole (g=9.832 m/s2).
a. What is his mass in Panama?
b. What is his weight in Panama?
c. What is his mass at the North Pole?
d. What is his weight at the North Pole?
4. You are driving around in your car one day. Your 1475 kg car is a very comfortable car to
ride in. You are driving at 50 m/s when you suddenly decide to accelerate to 65 m/s. It take
you 10 s to accelerate. What is the average net force that you have applied to the car?
5. A 200 kg box is pushed horizontally with a force of 700 N. If the coefficient of friction is 0.20,
calculate the acceleration of the box.
6. A sled of mass 50 kg is pulled along snow-covered, flat ground. The static friction
coefficient is 0.30, and the sliding friction coefficient is 0.10.
a. What does the sled weigh?
b. What force will be needed to start the sled moving?
c. What force is needed to keep the sled moving at a constant velocity?
d. Once moving, what total force must be applied to the sled to accelerate it 3.0 m/s2?
7. The maximum force a grocery sack can withstand and not rip is 250 N. If 20 kg of groceries
are lifted from the floor to the table with an acceleration of 5 m/s2, will the sack hold?
8. A car of mass 1330 kg is traveling at 28.0 m/s. The driver applies the brakes to bring the car
to rest over a distance of 79.0 m. Calculate the force acting on the car.
9. A 1500-kg car can accelerate from rest to 72 km/h in 8.0 s. What is the net force acting on
the car to cause this acceleration?
10. An elevator is moving down with an acceleration of 3.36 m/s2. What would be the apparent
weight of a 64.2-kg man in the elevator?
11. An elevator is moving up with an acceleration of 1.40 m/s2. A 14.5-kg block hangs from a
spring balance fixed to the roof of the elevator. What is the apparent weight of the block?
12. Three blocks A, B, and C are connected by two massless strings passing over smooth
pulleys as shown below, with the 3.4-kg block on a smooth horizontal surface. Calculate the
tension in the strings connecting A and B, and, B and C.
3.4 kg
6.9 kg
4.1 kg
13. A 2.1-kg block is kept on a 3.5-kg block resting on the floor of an elevator. If the elevator is
moving up at 1.1 m/s2, calculate the following:
a. Force exerted by the 2.1-kg block on the 3.5-kg block.
b. Force exerted by the floor of the elevator on the 3.5-kg block.
14. A man is standing on a scale inside an airplane. When the airplane is traveling horizontally
(in other words, the vertical acceleration of the plane is zero) the scale reads 705.6 N. What
is the vertical acceleration of the plane in each of the following situations?
a. When the scale reads 950.0 N
b. When the scale reads 500.0 N
Key
1. 12 m/s2
2. 15 m/s2
3. a. 105 kg
b. 1027.11 N
c. 105 kg
d. 1032.36 N
4. 2212.2 N
5. 1.54 m/s2
6. a. 490N
b. 149 N
c. 49 N
d. 199 N
7. No
8. -6599.49 N
9. 3750 N
10. -413.45N
11. 162.4N
12.
A and B 54.44 N
B and C 48.01 N
13.
a. 22.89N
b. 61.04N
14.
a. 3.39m/s2
b. -2.86m/s2