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victus00 [196]
3 years ago
14

Tourists covered 255 km for a 4-hour ride by car and a 7-hour ride by train. what is the speed of the train, if it is 5 km/h gre

ater than the speed of the car?
Physics
1 answer:
LekaFEV [45]3 years ago
4 0
The distance covered by car is equal to (assuming it is moving by uniform motion) the product between the car's speed and the time of the car ride, 4 h:
S_c = v_c t_c
where
v_c is the car's speed
t_c = 4 h is the duration of the car ride

Similarly, the distance covered by train is equal to the product between the train's speed and the duration of the train ride, 7 h:
S_t = v_t t_t

The total distance covered is S=255 km, which is the sum of the distances covered by car and train:
S=255 km = S_c + S_t
which becomes
255 = 4 v_c + 7 v_t (1)
we also know that the train speed is 5 km/h greater than the car's speed:
v_t = 5 + v_c (2)

If we put (2) into (1), we find
255 = 4v_c + 7(5+v_c)
and if we solve it, we find
v_c = 20 km/h
v_t = 25 km/h

So, the car speed is 20 km/h and the train speed is 25 km/h.

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Calculate the translational speed of a cylinder when it reaches the foot of an incline 7.05 mm high. Assume it starts from rest
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Height is 7.05 m and not 7.05 mm

Answer:

9.603 m/s

Explanation:

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v_cm = Rω

Since we are working with a solid cylinder, moment of inertia of the cylinder is; I = ½mR²

Since it is rolled from the top to the bottom, at the top it will have potential energy(mgh) while at the bottom it will have kinetic energy (rotational plus translational kinetic energy).

Using conservation of energy, we have:

P.E = K.E_t + K.E_r

Formula for rotational and kinetic energy here are;

K.E_t = ½mv²

K.E_r = ½Iω²

mgh = ½mv² + ½Iω²

Since we want to find translational speed(v), let's get rid of ω.

Earlier, we saw that v_cm = Rω

Thus; ω = v/R

Also, we know that I = ½mR².

Thus;

mgh = ½mv² + ½(½mR²)(v/R)²

This gives;

mgh = ½mv² + ¼mv²

Divide through by m to get;

gh = v²(½ + ¼)

gh = ¾v²

Making v the subject gives;

v = √(4gh/3)

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