- #1
freezx
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Hi
Can anybody correct my answers ?
1- when the speed of a moving object is doubled, its
a- Acceleration is doubled
b- Weight is doubled
c- Kinetic energy is double
d- Kinetic energy is increase four times
My answer is d
2- an iron sphere of mass 40 kg has the same diameter as an aluminium sphere whose mass is 10 kg. the sphere are dropped at the same time from a tower. When they are 115 m from the ground, they have the same:
a- Kinetic energy
b- Potential energy
c- Momentum
d- Impulse
e- Acceleration
My answer is a
3- how much work is done by a force of 10N in moving an object through a distance of 2 m in the direction of the force?
Work= force* distance
= 10 * 2 = 20 J
4- A bag of rice weighs 150 kg. to what height should it be raised so that its potential energy is 10 J ?
PE= mgh
10 = 150 * 9.8 * h
h = 10/(150 * 9.8) = 0.0068 m
5- calculates the work done in lifting 250 kg of water through a vertical height of 8 meters.
PE = mgh
= 250 * 9.8 * 8 = 19600 J
Work = PE
So work = 19600 J
6- A truck weighing 10000N and traveling at 35m/s stops at a distance of 40 m decelerating uniformly. What is the force exerted on it by the brakes? What is the work done by the brakes?
V2 = u2 + 2aS
u2 = -2 aS because the final speed is zero
1225 = - 2 * 40 * a
a = 1225/-80 = -15.31 m/s2
for the time
v = u + at
0 = 35 + (-15.31)* t
- 35 = ( -15.31 ) * t
t = -35/-15.31 = 2.28 s
force = mass * acceleration
10000 = mass * 9.8
mass = 10000/9.8 = 1020.4 kg
force exerted = mass * acceleration
= 1020.4 * - 15.31 = - 15622.32N
work done by the brakes:
work = force * distance
= 10000 * 40 = 400000 Joules
7- A man drops a 15 kg rock from a top of 20 m building. What is its speed just before it hits the ground? What is its kinetic energy when it reaches the ground?
PE= 15 * 9.8 * 20 = 2940 Joules
KE = PE
KE = ½ mv2
2940 = ½ * 15 * v2
2940 = 7.5 * v2
v2 = 2940/7.5
v = square root of ( 2940/7.5)
v = 19.79 m/s
KE= PE
So KE =2940 Joules
Can anybody correct my answers ?
1- when the speed of a moving object is doubled, its
a- Acceleration is doubled
b- Weight is doubled
c- Kinetic energy is double
d- Kinetic energy is increase four times
My answer is d
2- an iron sphere of mass 40 kg has the same diameter as an aluminium sphere whose mass is 10 kg. the sphere are dropped at the same time from a tower. When they are 115 m from the ground, they have the same:
a- Kinetic energy
b- Potential energy
c- Momentum
d- Impulse
e- Acceleration
My answer is a
3- how much work is done by a force of 10N in moving an object through a distance of 2 m in the direction of the force?
Work= force* distance
= 10 * 2 = 20 J
4- A bag of rice weighs 150 kg. to what height should it be raised so that its potential energy is 10 J ?
PE= mgh
10 = 150 * 9.8 * h
h = 10/(150 * 9.8) = 0.0068 m
5- calculates the work done in lifting 250 kg of water through a vertical height of 8 meters.
PE = mgh
= 250 * 9.8 * 8 = 19600 J
Work = PE
So work = 19600 J
6- A truck weighing 10000N and traveling at 35m/s stops at a distance of 40 m decelerating uniformly. What is the force exerted on it by the brakes? What is the work done by the brakes?
V2 = u2 + 2aS
u2 = -2 aS because the final speed is zero
1225 = - 2 * 40 * a
a = 1225/-80 = -15.31 m/s2
for the time
v = u + at
0 = 35 + (-15.31)* t
- 35 = ( -15.31 ) * t
t = -35/-15.31 = 2.28 s
force = mass * acceleration
10000 = mass * 9.8
mass = 10000/9.8 = 1020.4 kg
force exerted = mass * acceleration
= 1020.4 * - 15.31 = - 15622.32N
work done by the brakes:
work = force * distance
= 10000 * 40 = 400000 Joules
7- A man drops a 15 kg rock from a top of 20 m building. What is its speed just before it hits the ground? What is its kinetic energy when it reaches the ground?
PE= 15 * 9.8 * 20 = 2940 Joules
KE = PE
KE = ½ mv2
2940 = ½ * 15 * v2
2940 = 7.5 * v2
v2 = 2940/7.5
v = square root of ( 2940/7.5)
v = 19.79 m/s
KE= PE
So KE =2940 Joules