chapter 3 physical science
A 2-kg book is held 1 m above the floor for 50 s. The work done is
0
A 100-kg astronaut ejects 4 g of gas from her propulsion pistol at a speed of 50 m/s. Her recoil speed is
0.2 mm/s.
A horse has a power output of 1 hp (746 W) when it is pulling a cart. If the cart covers 100 m in 30 s, the force the horse exerts on the cart is
0.22 kN
The work you do in raising an orange from your waist to your mouth is roughly
1 J
A 1-kg mass has a KE of 1 J when its speed is
1.4 m/s
A 90-kg llama has an average power output of 80 W. The minimum time the llama can go up a hill 500 m high is
1.5 h
A weightlifter raises a 200-kg barbell through a height of 2 m in 2.2 s. The average power he develops during the lift is
1.78 kW
The mechanical advantage of a pair of scissors might be
1/2
A total of 4900 J is expended in lifting a 50-kg mass. The mass is raised to a height of
10 m
The KE of a 900-kg car whose speed is 60 km/h is
125 kJ
A 1-kg object is moving at 10 m/s. To double its kinetic energy, its speed should be increased to approximately
14 m/s
A horizontal force is applied to a 2-kg ball on a smooth table. The ball's speed is 8 m/s when it has gone 4 m. The magnitude of the force is
16 N
The minimum force that must be applied to a machine with a mechanical advantage of 5 in order to lift a 100-kg crate is
196 N
A 40-kg boy climbs a vertical ladder at 0.5 m/s. His power output is
196 W
A ball whose momentum is mv strikes a wall and bounces off. The change in the ball's momentum is
2 mv
When a ton of coal burns, it loses 3.3 × 10-7 kg of mass. The energy given off is
3.0 × 1010 J.
The speed of a 1000-kg car whose KE is 450 kJ is
30 m/s
The 2.5-kg head of an ax exerts a force of 80 kN as it penetrates 18 mm into the trunk of a tree. The speed of the ax head when it strikes the tree is
34 m/s
A 1-N weight has a KE of 1 J when its speed is
4.4 m/s
A 150-kg safe on frictionless casters is being raised 1.20 m to the bed of a truck using planks 4.00 m long. The force needed to push the safe up is
441 N
An 800-kg car moving at 80 km/h overtakes a 1200-kg car moving at 40 km/h in the same direction. If the two cars stick together, the wreckage has an initial speed of
56 km/h.
Six kJ of work is used to lift an object to a height of 100 m. The object's approximate mass is
6 kg
The mass equivalent of 6.0 MJ is
6.7 × 10-11 kg.
A sedentary person requires about 6 million J of energy per day. This rate of energy consumption is equivalent to about
70W
An 800-kg car moving at 80 km/h collides head-on with a 1200-kg car moving at 40 km/h in the opposite direction. If they stick together, the wreckage now has an initial speed of
8 km/h
According to the general theory of relativity, gravitation
is a distortion in space-time.
When the speed of an object is doubled,
its momentum is doubled
If a shell fired from a cannon explodes in midair,
its total KE increases.
Which of the following is (are) not a unit of power?
joule-second
An object that has linear momentum must also have
kinetic energy
If a spaceship 100 m long when at rest on the earth were to travel at nine-tenths the speed of light, its length as measured by an observer on the earth would be
less than 100 m.
In the formula E0 = mc2, the symbol c represents the speed of
light
A moving object does not necessarily have
potential energy
The watt is a unit of
power
A golf ball and a ping-pong ball are dropped in a vacuum chamber. When they have fallen halfway down, they have the same
speed
Which of the following quantities is always the same to all observers?
the speed of light in free space
What never changes when two or more objects collide is
the total momentum of all objects
The height above the ground of a child on a swing varies from 0.5 m at the lowest point to 2.0 m at the highest point. The maximum speed of the child is
about 5.4 m/s.
To prevent it from tumbling in flight, a projectile such as a football is sent off spinning. The physical principle involved is
conservation of angular momentum.
the sun
attracts light waves passing nearby.
