Question

A package was determined to have a mass of 5.7 kilograms. What's the force of gravity acting on the package on earth?

A. 37.93 N
B. 55.86 N
C. 1.72 N
D. 13.44 N

50 J of work was performed in 20 seconds. How much power was used to do this task?

A. 2.5 W
B. 4 W
C. 0.4 W
D. 24.5 W

A 63 kg object needs to be lifted 7 meters in a matter of 5 seconds. Approximately how much horsepower is required to achieve this task?

A. 864.36 hp
B. 1.16 hp
C. 441 hp
D. 0.59 hp

A force of 350 N causes a body to move with an acceleration of 10 m/s2. What's the mass of the body?

A. 98 kg
B. 35 kg
C. 3,500 kg
D. 3,430 kg

Which of the following statements is accurate?

A. If an object's velocity remains constant, its acceleration must be increasing.
B. If an object is said to be decelerating, its velocity must be increasing.
C. If an object's velocity decreases, then the object is accelerating.
D. If an object's velocity is changing, it's either experiencing acceleration or deceleration.

Answer 1

==> A package was determined . . .

Weight = (mass) x (gravity)

Gravity on Earth = 9.8 m/s²

Weight = (5.7 kg) x (9.8 m/s²)

= 55.86 kg-m/s² . 1 kg-m/s² = 1 N

==> 50 J of work was performed . . .

Power = (work done) / (time to do the work)

= (50 J) / (20 sec)

= 2.5 J/sec 1 J/sec = 1 watt

==> A 63-kg object needs . . .

Weight = (mass) x (gravity)
Work = (force) x (distance)
Power = (work done) / (time to do the work)

So Power = (mass) x (gravity) x (distance) / (time to lift)

= (63 kg) x (9.8 m/s²) x (7 m) / (5 sec)

= (63 x 9.8 x 7) / (5) (kg-m²/s²) / (sec)

= 864.36 joules/sec

Convert (864.36 watts) x (1 HP/746 watts) = 1.159 HP

(How to remember the conversion from watts to Horsepower:
The sails on Columbus' ship the Santa Maria developed 2 HP at top wind.
1492 / 2 = 746 watts per HP. )

==> A force of 350 N causes . . .

Force = (mass) x (acceleration)

Mass = (force) / (acceleration)

= (350 kg-m/s²) / (10 m/s²)

= 35 kg.

==> Which of the following . . .

Golden Rule: "Acceleration means any change in velocity,
including change in speed or direction."

A). No. Constant velocity means zero acceleration.
B). No. When people say "decelerating" they mean "slowing down".
That's decreasing magnitude of velocity.
C). Yes. 'Acceleration' does NOT mean 'speeding up'. Any change
in speed or direction, even slowing down, is acceleration.
D). Yes. If an object's velocity is changing, then either the speed or direction of its motion is changing, and either of those is 'acceleration'. The object doesn't need to be speeding up or slowing down, but if its direction is changing, then that's called 'acceleration. Rounding a curve at a constant speed, or driving a circle with constant speed, are both examples of 'acceleration'.

Answer 2

1.) The force of gravity is what we call weight, we define it as:
w=mg
w=5,7kg*9,8m/s²
w=55,86kg (b)
2.) We know that:
power=W/t
power=50J/20s
power=2,5Watts (a)
3.) The work done is equal to the potential energy, so:
Epg=mgh
Epg=63kg*9,8m/s²*7m
Epg=4321J
Now we get the power:
power=W/t
power=4321J/5s
power=864Watts
Now:
1HP=746Watts
=1,16HP (b)
4.) We know that:
F=ma
350N=m*10m/s²
m=350N/10m/s²
m=35kg (b)
5.) d.) Aceleration is tha rate of change in velocity, either positive (increasing) or negative (decreasing)