Balanced forces, equilibrium and inertia
Grade 11 Science Worksheet
Circle the best answer, or write your answer on the line.
A sign of mass 10 kg hangs from two cables, each 30° above the horizontal. To the nearest tenth of a newton, what is the tension in each cable, Ari?
A 10 kg sign hangs from two cables at 30° above the horizontal, each pulling 98 N. The cables are tightened to 10° above it. What happens to each tension, Jun?
- It rises to about 282 N, nearly three times the sign's weight
- It falls to about 49 N, since nearly flat cables hold less weight
- It stays 98 N, since the sign's weight has not changed
- It rises to about 100 N, since the angle changed by just 20°
A block stays at rest as a ramp is tilted from 20° to 40°. What happens to the normal force and to friction on it, Kira?
- The normal force increases while friction decreases
- The normal force stays equal to the weight, while friction increases
- The normal force decreases while friction increases
- Both increase, since the ramp is steeper than before
Free-body diagram (example data): a block on a frictionless 30° ramp, held by a rope parallel to the ramp. Using the free-body diagram, which pair of values is right for the rope and the ramp, Luz?
- Tension 24.5 N and normal force 49 N, the weight
- Tension 49 N, the weight, and normal force 42.4 N
- Tension 24.5 N and normal force 42.4 N
- Tension 42.4 N and normal force 24.5 N
A 70 kg skydiver falls at a steady 55 m/s. How big is the air's force on the diver, and which way, Milo?
- 686 N downward, in the same direction as the motion
- 0 N, since the diver is not accelerating at the moment
- 686 N upward, equal to the weight
- 3,850 N upward, from 70 × 55, to match the speed
A crate slides at a steady speed under an 80 N push. The push doubles to 160 N. What happens, Noah?
- It slows down, since a bigger push builds up more friction
- It slides at twice the speed, since speed follows the push
- It speeds up, since the net force is now about 80 N
- It stays at a steady speed, since friction rises to 160 N too
A 60 kg student stands on a scale in an elevator moving up at a steady 2 m/s. What does the scale read, Pia?
- 0 N, since the elevator is not accelerating
- 468 N, which takes 60 × 2 away from the weight
- 708 N, which adds 60 × 2 for the upward motion
- 588 N, the same as at rest
A bus brakes hard and a ball on its floor rolls toward the front. A rider says a forward force pushed it. What best explains the roll, Ren?
- Friction from the moving floor pushed the ball toward the front
- A forward force equal to the ball's inertia pushed it to the front
- The bus slowed but the ball kept moving; no forward force acted
- The ball's own inertia pushed it toward the front of the bus
A heavy ball hangs from a string, with a second string tied below it. Which string breaks first with a slow pull on the lower one, and with a sharp jerk, Tala?
- Slow pull: the lower string. Sharp jerk: the upper string
- Slow pull: the upper string. Sharp jerk: the lower string
- The lower string breaks first for both kinds of pull
- The upper string breaks first for both kinds of pull
A car cruises at 25 m/s as 400 N of engine force balances draw a line. The driver lifts off the gas. What happens next, Zee?
- It stops at once, since the engine force is gone
- It speeds up, since the drag now pushes the car along
- It slows, since 400 N of drag is no longer balanced
- It keeps 25 m/s, since its inertia carries it forward unchanged