Question

A 60 kg boy and 40 kg girl stand on skateboards on a frictionless, horizontal surface. The boy pushes the girl away from him. The girl gains a speed of 0.3 m/s during the 0.50 s the boy's hands are in contact with her.

- What will be the boy's speed after?
- Assuming that in each case the girl achieved the same speed, would it matter whether the boy pushed the girl, the girl pushed the boy, or they put their hands together and pushed each other away?

Answer #1

According to the law of conservation of linear momentum, the sum of intial andfinal momentum of a sytem is zero if there is no external force present.

Intially, the boy and girl are at rest. So, p_{i} is
zero.

After the boy pushes the girl away, the momentum of the girl
becomes p_{g}= 40*0.3 =12Kgm/s

Now according to the law of conservation of linear momentum,

_{Pi}=p_{f}

p_{i}=0 and
p_{f}=p_{b}+p_{g}

0=p_{b}+p_{g}

p_{b}=-p_{g}

m_{b}*v_{b}=-12

60*v_{b}=-12

v_{b}=-0.2m/s

So, the speed with which the boy goes is 0.2m/s.The negative sign is just for the reverse direction as from the girl.

It won't matter who pushes whom, if the girl gets the same speed of 0.3m/s then the boy gets the speed of 0.2m/s.

Two blocks with masses 3.0 kg and 5.0 kg are placed on a
horizontal frictionless surface. A light spring is placed in a
horizontal position between the blocks. The blocks are pushed
together, compressing the spring, and then released from rest.
After contact with the spring ends, the 5.0-kg mass has a speed of
2.0 m/s. How much potential energy was stored in the spring when
the blocks were released?

A 2.00 kg block slides on a frictionless, horizontal surface
with a speed of 5.10 m/s, until colliding head-on with, and
sticking to, a 1.00 kg block at rest. A) Find the speed of the
combination after the collision. B) The two blocks continue to
slide together until coming in contact with a horizontal spring and
eventually brought to rest. If the blocks compress the spring 10.0
cm, find the spring constant of the spring. C) How much work did...

A 0.300-kg puck, initially at rest on a horizontal, frictionless
surface, is struck by a 0.200-kg puck moving initially along the
x axis with a speed of 2.00 m/s. After the collision, the
0.200-kg puck has a speed of 1.00 m/s at an angle of ? =
49.0° to the positive x axis.
(a) Determine the velocity of the 0.300-kg puck after the
collision.
(b) Find the fraction of kinetic energy transferred away or
transformed to other forms of energy...

A 0.300-kg puck, initially at rest on a horizontal, frictionless
surface, is struck by a 0.200-kg puck moving initially along the x
axis with a speed of 2.00 m/s. After the collision, the 0.200- kg
puck has a speed of 1.00 m/s at an angle of θ = 53.0° to the
positive x axis. (a) Determine the velocity of the 0.300-kg puck
after the collision. (b) Find the fraction of kinetic energy lost
in the collision.

A 0.30-kg puck, initially at rest on a frictionless horizontal
surface, is struck by a 0.20-kg puck that is initially moving along
the x-axis with a velocity of 8.5 m/s. After the
collision, the 0.20-kg puck has a speed of 5.1 m/s at an angle
of
θ = 53°
to the positive x-axis.
(a) Determine the velocity of the 0.30-kg puck after the
collision.
magnitude
m/s
direction
° from the positive x-axis
(b) Find the fraction of kinetic energy lost...

A 0.50 kg mass sliding on a horizontal frictionless surface is
attached to one end of a horizontal spring (with k = 325 N/m) whose
other end is fixed. The mass has a kinetic energy of 16.0 J as it
passes through its equilibrium position (the point at which the
spring force is zero). At what rate is the spring doing work on the
mass as the mass passes through its equilibrium position?
At what rate is the spring doing...

If a 1 kg object on a horizontal, frictionless surface is
attached to a spring, displaced, and then released, it will
oscillate. If it is displaced 0.120 m from its equilibrium position
and released with zero initial speed. After 0.8 s its displacement
is found to be 0.120 m on the opposite side, and it has passed the
equilibrium position once during this interval. Find the amplitude,
the period, the frequency, the angular frequency and the spring
constant.

A 4.70-kg object on a frictionless horizontal surface is
attached to one end of a horizontal spring that has a force
constant k = 570 N/m. The spring is stretched 9.30 cm from
equilibrium and released.
(a) What is the frequency of the motion?
_____Hz
(b) What is the period of the motion?
______s
(c) What is the amplitude of the motion?
______cm
(d) What is the maximum speed of the motion?
______m/s
(e) What is the maximum acceleration of...

A small block on a frictionless, horizontal surface has a mass
of 2.50×10−2 kg . It is attached to a massless cord passing through
a hole in the surface (Figure 1) . The block is originally
revolving at a distance of 0.300 m from the hole with an angular
speed of 2.33 rad/s . The cord is then pulled from below,
shortening the radius of the circle in which the block revolves to
0.150 m. Model the block as a...

A small block on a frictionless, horizontal surface has a mass
of 2.90×10−2 kg . It is attached to a massless cord passing through
a hole in the surface (Figure 1). The block is originally revolving
at a distance of 0.300 m from the hole with an angular speed of
2.53 rad/s . The cord is then pulled from below, shortening the
radius of the circle in which the block revolves to 0.150 m. Model
the block as a particle....

ADVERTISEMENT

Get Answers For Free

Most questions answered within 1 hours.

ADVERTISEMENT

asked 5 minutes ago

asked 6 minutes ago

asked 6 minutes ago

asked 9 minutes ago

asked 9 minutes ago

asked 9 minutes ago

asked 10 minutes ago

asked 12 minutes ago

asked 14 minutes ago

asked 15 minutes ago

asked 15 minutes ago

asked 15 minutes ago